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authorVasiliy Kulikov <segoon@openwall.com>2011-07-26 23:08:38 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2011-07-26 23:49:43 (GMT)
commit293eb1e7772b25a93647c798c7b89bf26c2da2e0 (patch)
treedebd49012773091732ee1e1b2388462b759525a7
parentd2857e79a2ba7c155eaa1a7d3581c8d26b31e54e (diff)
proc: fix a race in do_io_accounting()
If an inode's mode permits opening /proc/PID/io and the resulting file descriptor is kept across execve() of a setuid or similar binary, the ptrace_may_access() check tries to prevent using this fd against the task with escalated privileges. Unfortunately, there is a race in the check against execve(). If execve() is processed after the ptrace check, but before the actual io information gathering, io statistics will be gathered from the privileged process. At least in theory this might lead to gathering sensible information (like ssh/ftp password length) that wouldn't be available otherwise. Holding task->signal->cred_guard_mutex while gathering the io information should protect against the race. The order of locking is similar to the one inside of ptrace_attach(): first goes cred_guard_mutex, then lock_task_sighand(). Signed-off-by: Vasiliy Kulikov <segoon@openwall.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/proc/base.c16
1 files changed, 13 insertions, 3 deletions
diff --git a/fs/proc/base.c b/fs/proc/base.c
index c9e3f65..08e3ecc 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2706,9 +2706,16 @@ static int do_io_accounting(struct task_struct *task, char *buffer, int whole)
{
struct task_io_accounting acct = task->ioac;
unsigned long flags;
+ int result;
- if (!ptrace_may_access(task, PTRACE_MODE_READ))
- return -EACCES;
+ result = mutex_lock_killable(&task->signal->cred_guard_mutex);
+ if (result)
+ return result;
+
+ if (!ptrace_may_access(task, PTRACE_MODE_READ)) {
+ result = -EACCES;
+ goto out_unlock;
+ }
if (whole && lock_task_sighand(task, &flags)) {
struct task_struct *t = task;
@@ -2719,7 +2726,7 @@ static int do_io_accounting(struct task_struct *task, char *buffer, int whole)
unlock_task_sighand(task, &flags);
}
- return sprintf(buffer,
+ result = sprintf(buffer,
"rchar: %llu\n"
"wchar: %llu\n"
"syscr: %llu\n"
@@ -2734,6 +2741,9 @@ static int do_io_accounting(struct task_struct *task, char *buffer, int whole)
(unsigned long long)acct.read_bytes,
(unsigned long long)acct.write_bytes,
(unsigned long long)acct.cancelled_write_bytes);
+out_unlock:
+ mutex_unlock(&task->signal->cred_guard_mutex);
+ return result;
}
static int proc_tid_io_accounting(struct task_struct *task, char *buffer)

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