diff options
| author | Dan Clash <daclash@linux.microsoft.com> | 2023-10-12 14:55:18 -0700 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2023-10-13 18:34:46 +0200 |
| commit | 03adc61edad49e1bbecfb53f7ea5d78f398fe368 (patch) | |
| tree | d1cb051e436c23759757d3cbc4162372ca91220a /fs | |
| parent | 94f6f0550c625fab1f373bb86a6669b45e9748b3 (diff) | |
audit,io_uring: io_uring openat triggers audit reference count underflow
An io_uring openat operation can update an audit reference count
from multiple threads resulting in the call trace below.
A call to io_uring_submit() with a single openat op with a flag of
IOSQE_ASYNC results in the following reference count updates.
These first part of the system call performs two increments that do not race.
do_syscall_64()
__do_sys_io_uring_enter()
io_submit_sqes()
io_openat_prep()
__io_openat_prep()
getname()
getname_flags() /* update 1 (increment) */
__audit_getname() /* update 2 (increment) */
The openat op is queued to an io_uring worker thread which starts the
opportunity for a race. The system call exit performs one decrement.
do_syscall_64()
syscall_exit_to_user_mode()
syscall_exit_to_user_mode_prepare()
__audit_syscall_exit()
audit_reset_context()
putname() /* update 3 (decrement) */
The io_uring worker thread performs one increment and two decrements.
These updates can race with the system call decrement.
io_wqe_worker()
io_worker_handle_work()
io_wq_submit_work()
io_issue_sqe()
io_openat()
io_openat2()
do_filp_open()
path_openat()
__audit_inode() /* update 4 (increment) */
putname() /* update 5 (decrement) */
__audit_uring_exit()
audit_reset_context()
putname() /* update 6 (decrement) */
The fix is to change the refcnt member of struct audit_names
from int to atomic_t.
kernel BUG at fs/namei.c:262!
Call Trace:
...
? putname+0x68/0x70
audit_reset_context.part.0.constprop.0+0xe1/0x300
__audit_uring_exit+0xda/0x1c0
io_issue_sqe+0x1f3/0x450
? lock_timer_base+0x3b/0xd0
io_wq_submit_work+0x8d/0x2b0
? __try_to_del_timer_sync+0x67/0xa0
io_worker_handle_work+0x17c/0x2b0
io_wqe_worker+0x10a/0x350
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/lkml/MW2PR2101MB1033FFF044A258F84AEAA584F1C9A@MW2PR2101MB1033.namprd21.prod.outlook.com/
Fixes: 5bd2182d58e9 ("audit,io_uring,io-wq: add some basic audit support to io_uring")
Signed-off-by: Dan Clash <daclash@linux.microsoft.com>
Link: https://lore.kernel.org/r/20231012215518.GA4048@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/namei.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/fs/namei.c b/fs/namei.c index 567ee547492b..94565bd7e73f 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -188,7 +188,7 @@ getname_flags(const char __user *filename, int flags, int *empty) } } - result->refcnt = 1; + atomic_set(&result->refcnt, 1); /* The empty path is special. */ if (unlikely(!len)) { if (empty) @@ -249,7 +249,7 @@ getname_kernel(const char * filename) memcpy((char *)result->name, filename, len); result->uptr = NULL; result->aname = NULL; - result->refcnt = 1; + atomic_set(&result->refcnt, 1); audit_getname(result); return result; @@ -261,9 +261,10 @@ void putname(struct filename *name) if (IS_ERR(name)) return; - BUG_ON(name->refcnt <= 0); + if (WARN_ON_ONCE(!atomic_read(&name->refcnt))) + return; - if (--name->refcnt > 0) + if (!atomic_dec_and_test(&name->refcnt)) return; if (name->name != name->iname) { |