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proc: Check /proc/$pid/attr/ writes against file opener

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commit bfb819ea20 upstream.

Fix another "confused deputy" weakness[1]. Writes to /proc/$pid/attr/
files need to check the opener credentials, since these fds do not
transition state across execve(). Without this, it is possible to
trick another process (which may have different credentials) to write
to its own /proc/$pid/attr/ files, leading to unexpected and possibly
exploitable behaviors.

[1] https://www.kernel.org/doc/html/latest/security/credentials.html?highlight=confused#open-file-credentials

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Kees Cook 2021-05-25 12:37:35 -07:00 • committed by Greg Kroah-Hartman
commit fb003a1bd6
1 changed files with 4 additions and 0 deletions
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4
fs/proc/base.c
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@ -2704,6 +2704,10 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
void *page;
int rv;
/* A task may only write when it was the opener. */
if (file->f_cred != current_real_cred())
return -EPERM;
rcu_read_lock();
task = pid_task(proc_pid(inode), PIDTYPE_PID);
if (!task) {