BUG_ON() in audit_syscall_entry() is hit under the following conditions: 1) syscall auditing is enabled (that is, by running auditd). 2) user process issues syscall(-1) In fact, syscall(-1) just fails (not raising SIGILL, that is an expected behavior if not audited), and the succeeding syscall will hit this BUG_ON.
------------[ cut here ]------------ kernel BUG at (...)/kernel/auditsc.c:1534! Internal error: Oops - BUG: 0 [#1] SMP ARM Modules linked in: CPU: 0 PID: 61 Comm: syscall_arm Not tainted 3.17.0-rc4 #60 task: ea0c4380 ti: ea48e000 task.ti: ea48e000 PC is at __audit_syscall_entry+0xe4/0x110 LR is at 0xea0c4380 pc : [<c02b2ae8>] lr : [<ea0c4380>] psr: 20000013 sp : ea48ff68 ip : 00000001 fp : 0000869c r10: 00000200 r9 : ea48e000 r8 : c020f4e4 r7 : 000000c5 r6 : ea48e000 r5 : ea48ffb0 r4 : ea490800 r3 : bef1e718 r2 : 00000001 r1 : 000000c5 r0 : 40000028 Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user Control: 10c5387d Table: 8a4ac059 DAC: 00000015 Process syscall_arm (pid: 61, stack limit = 0xea48e250) Stack: (0xea48ff68 to 0xea490000) ff60: 540e7a69 3ab5e840 00000200 000000c5 ea48ffb0 ea48e000 ff80: 000000c5 c02114bc bef1e718 00000001 b6efdb58 ffffffff 08400000 000000c5 ffa0: c020f4e4 c020f49c b6efdb58 ffffffff 00000001 bef1e718 bef1e718 00000001 ffc0: b6efdb58 ffffffff 08400000 000000c5 00000000 b6f22850 00000008 0000869c ffe0: 000000c5 bef1e704 b6ea315f b6e318e6 20000030 00000001 00000000 00000000 [<c02b2ae8>] (__audit_syscall_entry) from [<c02114bc>] (syscall_trace_enter+0xf0/0x120) [<c02114bc>] (syscall_trace_enter) from [<c020f49c>] (__sys_trace+0xc/0x38) Code: e584500c e5842004 e28dd00c e8bd80f0 (e7f001f2) ---[ end trace 0c4441660aba5692 ]---
Under the current implementation, audit_syscall_entry() is called even against syscall(-1), but audit_syscall_exit() is not. Because 'in_syscall' flag in a current thread's audit context is kept on, next called audit_syscall_entry() will see BUG_ON(in_syscall).
This patch fixes this bug by 1) preventing syscall enter/exit tracing, ftrace tracepoint and audit, from being executed if an invalid (including -1) or pseudo syscall number (starting from __NR_ARM_BASE + 1). Please note that tracehook_report_syscall(PTRACE_SYSCALL_EXIT) is still executed as it should be paired with tracehook_report_syscall(PTRACE_SYSCALL_ENTER).
2) handling user-issued syscall(-1) with arm_syscall() for compatibility if tracing is on. Since UL(-1) > __NR_ARM_BASE - __NR_SYSCALL_BASE, arm_syscall() is called at local_restart in entry-common.S if tracing is off.
Signed-off-by: AKASHI Takahiro takahiro.akashi@linaro.org --- arch/arm/include/asm/traps.h | 1 + arch/arm/kernel/entry-common.S | 3 ++- arch/arm/kernel/ptrace.c | 49 +++++++++++++++++++++++++--------------- 3 files changed, 34 insertions(+), 19 deletions(-)
diff --git a/arch/arm/include/asm/traps.h b/arch/arm/include/asm/traps.h index f555bb3..de01145 100644 --- a/arch/arm/include/asm/traps.h +++ b/arch/arm/include/asm/traps.h @@ -49,6 +49,7 @@ static inline int in_exception_text(unsigned long ptr) extern void __init early_trap_init(void *); extern void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame); extern void ptrace_break(struct task_struct *tsk, struct pt_regs *regs); +extern int arm_syscall(int no, struct pt_regs *regs);
extern void *vectors_page;
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S index e52fe5a..4c62324 100644 --- a/arch/arm/kernel/entry-common.S +++ b/arch/arm/kernel/entry-common.S @@ -476,10 +476,11 @@ __sys_trace: cmp scno, #-1 @ skip the syscall? bne 2b add sp, sp, #S_OFF @ restore stack - b ret_slow_syscall + b __sys_trace_return_skipped
__sys_trace_return: str r0, [sp, #S_R0 + S_OFF]! @ save returned r0 +__sys_trace_return_skipped: mov r0, sp bl syscall_trace_exit b ret_slow_syscall diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c index 0c27ed6..d458367 100644 --- a/arch/arm/kernel/ptrace.c +++ b/arch/arm/kernel/ptrace.c @@ -930,7 +930,9 @@ static void tracehook_report_syscall(struct pt_regs *regs,
asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) { - current_thread_info()->syscall = scno; + int orig_scno; + + current_thread_info()->syscall = orig_scno = scno;
/* Do the secure computing check first; failures should be fast. */ if (secure_computing(scno) == -1) @@ -941,31 +943,42 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
scno = current_thread_info()->syscall;
- if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) - trace_sys_enter(regs, scno); + if (scno >= 0 && scno < NR_syscalls) { + if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) + trace_sys_enter(regs, scno);
- audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0, regs->ARM_r1, - regs->ARM_r2, regs->ARM_r3); + audit_syscall_entry(AUDIT_ARCH_ARM, scno, + regs->ARM_r0, regs->ARM_r1, + regs->ARM_r2, regs->ARM_r3); + } else if (scno == -1 && orig_scno == -1) { + /* + * For compatibility, we handles user-issued syscall(-1) + * here with arm_syscall(). + */ + arm_syscall(scno, regs); + }
return scno; }
asmlinkage void syscall_trace_exit(struct pt_regs *regs) { - /* - * Audit the syscall before anything else, as a debugger may - * come in and change the current registers. - */ - audit_syscall_exit(regs); + if (current_thread_info()->syscall < NR_syscalls) { + /* + * Audit the syscall before anything else, as a debugger may + * come in and change the current registers. + */ + audit_syscall_exit(regs);
- /* - * Note that we haven't updated the ->syscall field for the - * current thread. This isn't a problem because it will have - * been set on syscall entry and there hasn't been an opportunity - * for a PTRACE_SET_SYSCALL since then. - */ - if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) - trace_sys_exit(regs, regs_return_value(regs)); + /* + * Note that we haven't updated the ->syscall field for the + * current thread. This isn't a problem because it will have + * been set on syscall entry and there hasn't been + * an opportunity for a PTRACE_SET_SYSCALL since then. + */ + if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) + trace_sys_exit(regs, regs_return_value(regs)); + }
if (test_thread_flag(TIF_SYSCALL_TRACE)) tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);
On Wed, Oct 1, 2014 at 3:45 AM, AKASHI Takahiro takahiro.akashi@linaro.org wrote:
BUG_ON() in audit_syscall_entry() is hit under the following conditions:
- syscall auditing is enabled (that is, by running auditd).
- user process issues syscall(-1)
In fact, syscall(-1) just fails (not raising SIGILL, that is an expected behavior if not audited), and the succeeding syscall will hit this BUG_ON.
Thanks for digging in to this!
------------[ cut here ]------------ kernel BUG at (...)/kernel/auditsc.c:1534! Internal error: Oops - BUG: 0 [#1] SMP ARM Modules linked in: CPU: 0 PID: 61 Comm: syscall_arm Not tainted 3.17.0-rc4 #60 task: ea0c4380 ti: ea48e000 task.ti: ea48e000 PC is at __audit_syscall_entry+0xe4/0x110 LR is at 0xea0c4380 pc : [<c02b2ae8>] lr : [<ea0c4380>] psr: 20000013 sp : ea48ff68 ip : 00000001 fp : 0000869c r10: 00000200 r9 : ea48e000 r8 : c020f4e4 r7 : 000000c5 r6 : ea48e000 r5 : ea48ffb0 r4 : ea490800 r3 : bef1e718 r2 : 00000001 r1 : 000000c5 r0 : 40000028 Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user Control: 10c5387d Table: 8a4ac059 DAC: 00000015 Process syscall_arm (pid: 61, stack limit = 0xea48e250) Stack: (0xea48ff68 to 0xea490000) ff60: 540e7a69 3ab5e840 00000200 000000c5 ea48ffb0 ea48e000 ff80: 000000c5 c02114bc bef1e718 00000001 b6efdb58 ffffffff 08400000 000000c5 ffa0: c020f4e4 c020f49c b6efdb58 ffffffff 00000001 bef1e718 bef1e718 00000001 ffc0: b6efdb58 ffffffff 08400000 000000c5 00000000 b6f22850 00000008 0000869c ffe0: 000000c5 bef1e704 b6ea315f b6e318e6 20000030 00000001 00000000 00000000 [<c02b2ae8>] (__audit_syscall_entry) from [<c02114bc>] (syscall_trace_enter+0xf0/0x120) [<c02114bc>] (syscall_trace_enter) from [<c020f49c>] (__sys_trace+0xc/0x38) Code: e584500c e5842004 e28dd00c e8bd80f0 (e7f001f2) ---[ end trace 0c4441660aba5692 ]---
Under the current implementation, audit_syscall_entry() is called even against syscall(-1), but audit_syscall_exit() is not. Because 'in_syscall' flag in a current thread's audit context is kept on, next called audit_syscall_entry() will see BUG_ON(in_syscall).
This patch fixes this bug by
preventing syscall enter/exit tracing, ftrace tracepoint and audit, from being executed if an invalid (including -1) or pseudo syscall number (starting from __NR_ARM_BASE + 1). Please note that tracehook_report_syscall(PTRACE_SYSCALL_EXIT) is still executed as it should be paired with tracehook_report_syscall(PTRACE_SYSCALL_ENTER).
handling user-issued syscall(-1) with arm_syscall() for compatibility if tracing is on. Since UL(-1) > __NR_ARM_BASE - __NR_SYSCALL_BASE, arm_syscall() is called at local_restart in entry-common.S if tracing is off.
Signed-off-by: AKASHI Takahiro takahiro.akashi@linaro.org
arch/arm/include/asm/traps.h | 1 + arch/arm/kernel/entry-common.S | 3 ++- arch/arm/kernel/ptrace.c | 49 +++++++++++++++++++++++++--------------- 3 files changed, 34 insertions(+), 19 deletions(-)
diff --git a/arch/arm/include/asm/traps.h b/arch/arm/include/asm/traps.h index f555bb3..de01145 100644 --- a/arch/arm/include/asm/traps.h +++ b/arch/arm/include/asm/traps.h @@ -49,6 +49,7 @@ static inline int in_exception_text(unsigned long ptr) extern void __init early_trap_init(void *); extern void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame); extern void ptrace_break(struct task_struct *tsk, struct pt_regs *regs); +extern int arm_syscall(int no, struct pt_regs *regs);
extern void *vectors_page;
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S index e52fe5a..4c62324 100644 --- a/arch/arm/kernel/entry-common.S +++ b/arch/arm/kernel/entry-common.S @@ -476,10 +476,11 @@ __sys_trace: cmp scno, #-1 @ skip the syscall? bne 2b add sp, sp, #S_OFF @ restore stack
b ret_slow_syscall
b __sys_trace_return_skipped__sys_trace_return: str r0, [sp, #S_R0 + S_OFF]! @ save returned r0 +__sys_trace_return_skipped: mov r0, sp bl syscall_trace_exit b ret_slow_syscall diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c index 0c27ed6..d458367 100644 --- a/arch/arm/kernel/ptrace.c +++ b/arch/arm/kernel/ptrace.c @@ -930,7 +930,9 @@ static void tracehook_report_syscall(struct pt_regs *regs,
asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) {
current_thread_info()->syscall = scno;
int orig_scno;current_thread_info()->syscall = orig_scno = scno; /* Do the secure computing check first; failures should be fast. */ if (secure_computing(scno) == -1)@@ -941,31 +943,42 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
scno = current_thread_info()->syscall;
if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))trace_sys_enter(regs, scno);
if (scno >= 0 && scno < NR_syscalls) {if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))trace_sys_enter(regs, scno);
audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0, regs->ARM_r1,regs->ARM_r2, regs->ARM_r3);
audit_syscall_entry(AUDIT_ARCH_ARM, scno,regs->ARM_r0, regs->ARM_r1,regs->ARM_r2, regs->ARM_r3);} else if (scno == -1 && orig_scno == -1) {/** For compatibility, we handles user-issued syscall(-1)* here with arm_syscall().*/arm_syscall(scno, regs);
Won't this always land in bad_syscall(-1, regs) during arm_syscall? Should syscall_trace-enter just call bad_syscall directly instead, or are you using arm_syscall since it's the common entry point for this kind of logic on "non-standard" syscalls?
Either way, this look good! Thanks!
Reviewed-by: Kees Cook keescook@chromium.org
-Kees
} return scno;}
asmlinkage void syscall_trace_exit(struct pt_regs *regs) {
/** Audit the syscall before anything else, as a debugger may* come in and change the current registers.*/audit_syscall_exit(regs);
if (current_thread_info()->syscall < NR_syscalls) {/** Audit the syscall before anything else, as a debugger may* come in and change the current registers.*/audit_syscall_exit(regs);
/** Note that we haven't updated the ->syscall field for the* current thread. This isn't a problem because it will have* been set on syscall entry and there hasn't been an opportunity* for a PTRACE_SET_SYSCALL since then.*/if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))trace_sys_exit(regs, regs_return_value(regs));
/** Note that we haven't updated the ->syscall field for the* current thread. This isn't a problem because it will have* been set on syscall entry and there hasn't been* an opportunity for a PTRACE_SET_SYSCALL since then.*/if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))trace_sys_exit(regs, regs_return_value(regs));} if (test_thread_flag(TIF_SYSCALL_TRACE)) tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);-- 1.7.9.5
On 14/10/01, AKASHI Takahiro wrote:
BUG_ON() in audit_syscall_entry() is hit under the following conditions:
- syscall auditing is enabled (that is, by running auditd).
- user process issues syscall(-1)
In fact, syscall(-1) just fails (not raising SIGILL, that is an expected behavior if not audited), and the succeeding syscall will hit this BUG_ON.
Ok, this looks related to: https://lkml.org/lkml/2014/6/16/682
Andy has another plan for upstream: https://lkml.org/lkml/2014/6/16/730
Which finally got posted here: https://lkml.org/lkml/2014/9/5/736 v5 0/5 x86: two-phase syscall tracing and seccomp fastpath
This is all x86 stuff, but sounds like it may be a problem across other architectures as well.
Thanks for testing this!
------------[ cut here ]------------ kernel BUG at (...)/kernel/auditsc.c:1534! Internal error: Oops - BUG: 0 [#1] SMP ARM Modules linked in: CPU: 0 PID: 61 Comm: syscall_arm Not tainted 3.17.0-rc4 #60 task: ea0c4380 ti: ea48e000 task.ti: ea48e000 PC is at __audit_syscall_entry+0xe4/0x110 LR is at 0xea0c4380 pc : [<c02b2ae8>] lr : [<ea0c4380>] psr: 20000013 sp : ea48ff68 ip : 00000001 fp : 0000869c r10: 00000200 r9 : ea48e000 r8 : c020f4e4 r7 : 000000c5 r6 : ea48e000 r5 : ea48ffb0 r4 : ea490800 r3 : bef1e718 r2 : 00000001 r1 : 000000c5 r0 : 40000028 Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user Control: 10c5387d Table: 8a4ac059 DAC: 00000015 Process syscall_arm (pid: 61, stack limit = 0xea48e250) Stack: (0xea48ff68 to 0xea490000) ff60: 540e7a69 3ab5e840 00000200 000000c5 ea48ffb0 ea48e000 ff80: 000000c5 c02114bc bef1e718 00000001 b6efdb58 ffffffff 08400000 000000c5 ffa0: c020f4e4 c020f49c b6efdb58 ffffffff 00000001 bef1e718 bef1e718 00000001 ffc0: b6efdb58 ffffffff 08400000 000000c5 00000000 b6f22850 00000008 0000869c ffe0: 000000c5 bef1e704 b6ea315f b6e318e6 20000030 00000001 00000000 00000000 [<c02b2ae8>] (__audit_syscall_entry) from [<c02114bc>] (syscall_trace_enter+0xf0/0x120) [<c02114bc>] (syscall_trace_enter) from [<c020f49c>] (__sys_trace+0xc/0x38) Code: e584500c e5842004 e28dd00c e8bd80f0 (e7f001f2) ---[ end trace 0c4441660aba5692 ]---
Under the current implementation, audit_syscall_entry() is called even against syscall(-1), but audit_syscall_exit() is not. Because 'in_syscall' flag in a current thread's audit context is kept on, next called audit_syscall_entry() will see BUG_ON(in_syscall).
This patch fixes this bug by
preventing syscall enter/exit tracing, ftrace tracepoint and audit, from being executed if an invalid (including -1) or pseudo syscall number (starting from __NR_ARM_BASE + 1). Please note that tracehook_report_syscall(PTRACE_SYSCALL_EXIT) is still executed as it should be paired with tracehook_report_syscall(PTRACE_SYSCALL_ENTER).
handling user-issued syscall(-1) with arm_syscall() for compatibility if tracing is on. Since UL(-1) > __NR_ARM_BASE - __NR_SYSCALL_BASE, arm_syscall() is called at local_restart in entry-common.S if tracing is off.
Signed-off-by: AKASHI Takahiro takahiro.akashi@linaro.org
arch/arm/include/asm/traps.h | 1 + arch/arm/kernel/entry-common.S | 3 ++- arch/arm/kernel/ptrace.c | 49 +++++++++++++++++++++++++--------------- 3 files changed, 34 insertions(+), 19 deletions(-)
diff --git a/arch/arm/include/asm/traps.h b/arch/arm/include/asm/traps.h index f555bb3..de01145 100644 --- a/arch/arm/include/asm/traps.h +++ b/arch/arm/include/asm/traps.h @@ -49,6 +49,7 @@ static inline int in_exception_text(unsigned long ptr) extern void __init early_trap_init(void *); extern void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame); extern void ptrace_break(struct task_struct *tsk, struct pt_regs *regs); +extern int arm_syscall(int no, struct pt_regs *regs); extern void *vectors_page; diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S index e52fe5a..4c62324 100644 --- a/arch/arm/kernel/entry-common.S +++ b/arch/arm/kernel/entry-common.S @@ -476,10 +476,11 @@ __sys_trace: cmp scno, #-1 @ skip the syscall? bne 2b add sp, sp, #S_OFF @ restore stack
- b ret_slow_syscall
- b __sys_trace_return_skipped
__sys_trace_return: str r0, [sp, #S_R0 + S_OFF]! @ save returned r0 +__sys_trace_return_skipped: mov r0, sp bl syscall_trace_exit b ret_slow_syscall diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c index 0c27ed6..d458367 100644 --- a/arch/arm/kernel/ptrace.c +++ b/arch/arm/kernel/ptrace.c @@ -930,7 +930,9 @@ static void tracehook_report_syscall(struct pt_regs *regs, asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) {
- current_thread_info()->syscall = scno;
- int orig_scno;
- current_thread_info()->syscall = orig_scno = scno;
/* Do the secure computing check first; failures should be fast. */ if (secure_computing(scno) == -1) @@ -941,31 +943,42 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) scno = current_thread_info()->syscall;
- if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
trace_sys_enter(regs, scno);
- if (scno >= 0 && scno < NR_syscalls) {
if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))trace_sys_enter(regs, scno);
- audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0, regs->ARM_r1,
regs->ARM_r2, regs->ARM_r3);
audit_syscall_entry(AUDIT_ARCH_ARM, scno,regs->ARM_r0, regs->ARM_r1,regs->ARM_r2, regs->ARM_r3);- } else if (scno == -1 && orig_scno == -1) {
/** For compatibility, we handles user-issued syscall(-1)* here with arm_syscall().*/arm_syscall(scno, regs);- }
return scno; } asmlinkage void syscall_trace_exit(struct pt_regs *regs) {
- /*
* Audit the syscall before anything else, as a debugger may* come in and change the current registers.*/- audit_syscall_exit(regs);
- if (current_thread_info()->syscall < NR_syscalls) {
/** Audit the syscall before anything else, as a debugger may* come in and change the current registers.*/audit_syscall_exit(regs);
- /*
* Note that we haven't updated the ->syscall field for the* current thread. This isn't a problem because it will have* been set on syscall entry and there hasn't been an opportunity* for a PTRACE_SET_SYSCALL since then.*/- if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
trace_sys_exit(regs, regs_return_value(regs));
/** Note that we haven't updated the ->syscall field for the* current thread. This isn't a problem because it will have* been set on syscall entry and there hasn't been* an opportunity for a PTRACE_SET_SYSCALL since then.*/if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))trace_sys_exit(regs, regs_return_value(regs));- }
if (test_thread_flag(TIF_SYSCALL_TRACE)) tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT); -- 1.7.9.5
- RGB
-- Richard Guy Briggs rbriggs@redhat.com Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat Remote, Ottawa, Canada Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
linaro-kernel@lists.linaro.org
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