3.16.57-rc1 review patch. If anyone has any objections, please let me know.
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From: Joe Lawrence joe.lawrence@redhat.com
commit 7a8d181949fb2c16be00f8cdb354794a30e46b39 upstream.
pipe_max_size is assigned directly via procfs sysctl:
static struct ctl_table fs_table[] = { ... { .procname = "pipe-max-size", .data = &pipe_max_size, .maxlen = sizeof(int), .mode = 0644, .proc_handler = &pipe_proc_fn, .extra1 = &pipe_min_size, }, ...
int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf, size_t *lenp, loff_t *ppos) { ... ret = proc_dointvec_minmax(table, write, buf, lenp, ppos) ...
and then later rounded in-place a few statements later:
... pipe_max_size = round_pipe_size(pipe_max_size); ...
This leaves a window of time between initial assignment and rounding that may be visible to other threads. (For example, one thread sets a non-rounded value to pipe_max_size while another reads its value.)
Similar reads of pipe_max_size are potentially racy:
pipe.c :: alloc_pipe_info() pipe.c :: pipe_set_size()
Add a new proc_dopipe_max_size() that consolidates reading the new value from the user buffer, verifying bounds, and calling round_pipe_size() with a single assignment to pipe_max_size.
Link: http://lkml.kernel.org/r/1507658689-11669-4-git-send-email-joe.lawrence@redh... Signed-off-by: Joe Lawrence joe.lawrence@redhat.com Reported-by: Mikulas Patocka mpatocka@redhat.com Reviewed-by: Mikulas Patocka mpatocka@redhat.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Jens Axboe axboe@kernel.dk Cc: Michael Kerrisk mtk.manpages@gmail.com Cc: Randy Dunlap rdunlap@infradead.org Cc: Josh Poimboeuf jpoimboe@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [bwh: Backported to 3.16: Continue using int sysctl functions because we don't have proper unsigned int support] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/fs/pipe.c +++ b/fs/pipe.c @@ -1008,7 +1008,7 @@ const struct file_operations pipefifo_fo * Currently we rely on the pipe array holding a power-of-2 number * of pages. Returns 0 on error. */ -static inline unsigned int round_pipe_size(unsigned int size) +unsigned int round_pipe_size(unsigned int size) { unsigned long nr_pages;
@@ -1112,25 +1112,13 @@ out_revert_acct: }
/* - * This should work even if CONFIG_PROC_FS isn't set, as proc_dointvec_minmax + * This should work even if CONFIG_PROC_FS isn't set, as proc_dopipe_max_size * will return an error. */ int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf, size_t *lenp, loff_t *ppos) { - unsigned int rounded_pipe_max_size; - int ret; - - ret = proc_dointvec_minmax(table, write, buf, lenp, ppos); - if (ret < 0 || !write) - return ret; - - rounded_pipe_max_size = round_pipe_size(pipe_max_size); - if (rounded_pipe_max_size == 0) - return -EINVAL; - - pipe_max_size = rounded_pipe_max_size; - return ret; + return proc_dopipe_max_size(table, write, buf, lenp, ppos); }
/* --- a/include/linux/pipe_fs_i.h +++ b/include/linux/pipe_fs_i.h @@ -149,5 +149,6 @@ long pipe_fcntl(struct file *, unsigned struct pipe_inode_info *get_pipe_info(struct file *file);
int create_pipe_files(struct file **, int); +unsigned int round_pipe_size(unsigned int size);
#endif --- a/include/linux/sysctl.h +++ b/include/linux/sysctl.h @@ -45,6 +45,9 @@ extern int proc_dointvec(struct ctl_tabl void __user *, size_t *, loff_t *); extern int proc_dointvec_minmax(struct ctl_table *, int, void __user *, size_t *, loff_t *); +extern int proc_dopipe_max_size(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos); extern int proc_dointvec_jiffies(struct ctl_table *, int, void __user *, size_t *, loff_t *); extern int proc_dointvec_userhz_jiffies(struct ctl_table *, int, --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -64,6 +64,7 @@ #include <linux/sched/sysctl.h> #include <linux/kexec.h> #include <linux/mount.h> +#include <linux/pipe_fs_i.h>
#include <asm/uaccess.h> #include <asm/processor.h> @@ -2222,6 +2223,47 @@ int proc_dointvec_minmax(struct ctl_tabl do_proc_dointvec_minmax_conv, ¶m); }
+struct do_proc_dopipe_max_size_conv_param { + unsigned int *min; +}; + +static int do_proc_dopipe_max_size_conv(bool *negp, unsigned long *lvalp, + int *valp, int write, void *data) +{ + struct do_proc_dopipe_max_size_conv_param *param = data; + + if (write) { + unsigned int val = round_pipe_size(*lvalp); + + if (*negp || val == 0) + return -EINVAL; + + if (param->min && *param->min > val) + return -ERANGE; + + if (*lvalp > UINT_MAX) + return -EINVAL; + + *valp = val; + } else { + unsigned int val = *valp; + *negp = false; + *lvalp = (unsigned long) val; + } + + return 0; +} + +int proc_dopipe_max_size(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + struct do_proc_dopipe_max_size_conv_param param = { + .min = (unsigned int *) table->extra1, + }; + return do_proc_dointvec(table, write, buffer, lenp, ppos, + do_proc_dopipe_max_size_conv, ¶m); +} + static void validate_coredump_safety(void) { #ifdef CONFIG_COREDUMP @@ -2737,6 +2779,12 @@ int proc_dointvec_minmax(struct ctl_tabl return -ENOSYS; }
+int proc_dopipe_max_size(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + return -ENOSYS; +} + int proc_dointvec_jiffies(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos) { @@ -2778,6 +2826,7 @@ int proc_doulongvec_ms_jiffies_minmax(st EXPORT_SYMBOL(proc_dointvec); EXPORT_SYMBOL(proc_dointvec_jiffies); EXPORT_SYMBOL(proc_dointvec_minmax); +EXPORT_SYMBOL_GPL(proc_dopipe_max_size); EXPORT_SYMBOL(proc_dointvec_userhz_jiffies); EXPORT_SYMBOL(proc_dointvec_ms_jiffies); EXPORT_SYMBOL(proc_dostring);