Starting with gcc-8.1, we get a warning about all system call definitions, which use an alias between functions with incompatible prototypes, e.g.:

In file included from ../mm/process_vm_access.c:19: ../include/linux/syscalls.h:211:18: warning: 'sys_process_vm_readv' alias between functions of incompatible types 'long int(pid_t, const struct iovec *, long unsigned int, const struct iovec *, long unsigned int, long unsigned int)' {aka 'long int(int, const struct iovec *, long unsigned int, const struct iovec *, long unsigned int, long unsigned int)'} and 'long int(long int, long int, long int, long int, long int, long int)' [-Wattribute-alias] asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \ ^~~ ../include/linux/syscalls.h:207:2: note: in expansion of macro '__SYSCALL_DEFINEx' __SYSCALL_DEFINEx(x, sname, __VA_ARGS__) ^~~~~~~~~~~~~~~~~ ../include/linux/syscalls.h:201:36: note: in expansion of macro 'SYSCALL_DEFINEx' #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, __VA_ARGS__) ^~~~~~~~~~~~~~~ ../mm/process_vm_access.c:300:1: note: in expansion of macro 'SYSCALL_DEFINE6' SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec, ^~~~~~~~~~~~~~~ ../include/linux/syscalls.h:215:18: note: aliased declaration here asmlinkage long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \ ^~~ ../include/linux/syscalls.h:207:2: note: in expansion of macro '__SYSCALL_DEFINEx' __SYSCALL_DEFINEx(x, sname, __VA_ARGS__) ^~~~~~~~~~~~~~~~~ ../include/linux/syscalls.h:201:36: note: in expansion of macro 'SYSCALL_DEFINEx' #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, __VA_ARGS__) ^~~~~~~~~~~~~~~ ../mm/process_vm_access.c:300:1: note: in expansion of macro 'SYSCALL_DEFINE6' SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,

This is really noisy and does not indicate a real problem. In the latest mainline kernel, this was addressed by commit bee20031772a ("disable -Wattribute-alias warning for SYSCALL_DEFINEx()"), which seems too invasive to backport.

This takes a much simpler approach and just disables the warning across the kernel.

Signed-off-by: Arnd Bergmann arnd@arndb.de --- Makefile | 1 + 1 file changed, 1 insertion(+)

diff --git a/Makefile b/Makefile index 54690fee0485..4812b35df210 100644 --- a/Makefile +++ b/Makefile @@ -624,6 +624,7 @@ KBUILD_CFLAGS += $(call cc-disable-warning,frame-address,) KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation) KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow) KBUILD_CFLAGS += $(call cc-disable-warning, int-in-bool-context) +KBUILD_CFLAGS += $(call cc-disable-warning, attribute-alias)

ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE KBUILD_CFLAGS += -Os

Commit 3756f6401c302617c5e091081ca4d26ab604bec5 upstream.

gcc-8 warns about using strncpy() with the source size as the limit:

fs/exec.c:1223:32: error: argument to 'sizeof' in 'strncpy' call is the same expression as the source; did you mean to use the size of the destination? [-Werror=sizeof-pointer-memaccess]

This is indeed slightly suspicious, as it protects us from source arguments without NUL-termination, but does not guarantee that the destination is terminated.

This keeps the strncpy() to ensure we have properly padded target buffer, but ensures that we use the correct length, by passing the actual length of the destination buffer as well as adding a build-time check to ensure it is exactly TASK_COMM_LEN.

There are only 23 callsites which I all reviewed to ensure this is currently the case. We could get away with doing only the check or passing the right length, but it doesn't hurt to do both.

Link: http://lkml.kernel.org/r/20171205151724.1764896-1-arnd@arndb.de Signed-off-by: Arnd Bergmann arnd@arndb.de Suggested-by: Kees Cook keescook@chromium.org Acked-by: Kees Cook keescook@chromium.org Acked-by: Ingo Molnar mingo@kernel.org Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Peter Zijlstra peterz@infradead.org Cc: Serge Hallyn serge@hallyn.com Cc: James Morris james.l.morris@oracle.com Cc: Aleksa Sarai asarai@suse.de Cc: "Eric W. Biederman" ebiederm@xmission.com Cc: Frederic Weisbecker frederic@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Arnd Bergmann arnd@arndb.de --- fs/exec.c | 7 +++---- include/linux/sched.h | 6 +++++- 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c index b8c43be24751..fcd8642ef2d2 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1228,15 +1228,14 @@ static int de_thread(struct task_struct *tsk) return -EAGAIN; }

-char *get_task_comm(char *buf, struct task_struct *tsk) +char *__get_task_comm(char *buf, size_t buf_size, struct task_struct *tsk) { - /* buf must be at least sizeof(tsk->comm) in size */ task_lock(tsk); - strncpy(buf, tsk->comm, sizeof(tsk->comm)); + strncpy(buf, tsk->comm, buf_size); task_unlock(tsk); return buf; } -EXPORT_SYMBOL_GPL(get_task_comm); +EXPORT_SYMBOL_GPL(__get_task_comm);

/* * These functions flushes out all traces of the currently running executable diff --git a/include/linux/sched.h b/include/linux/sched.h index 5ebef8c86c26..1cc5723a7821 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2999,7 +2999,11 @@ static inline void set_task_comm(struct task_struct *tsk, const char *from) { __set_task_comm(tsk, from, false); } -extern char *get_task_comm(char *to, struct task_struct *tsk); +extern char *__get_task_comm(char *to, size_t len, struct task_struct *tsk); +#define get_task_comm(buf, tsk) ({ \ + BUILD_BUG_ON(sizeof(buf) != TASK_COMM_LEN); \ + __get_task_comm(buf, sizeof(buf), tsk); \ +})

#ifdef CONFIG_SMP void scheduler_ipi(void);