Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

fs/super: fix emergency thaw double-unlock of s_umount

do_thaw_all() iterates over all superblocks via __iterate_supers() with SUPER_ITER_EXCL, which acquires s_umount exclusively before calling the callback and releases it afterwards. However, the callback do_thaw_all_callback() calls thaw_super_locked() which unconditionally releases s_umount on every code path. This results in a second unlock attempt in __iterate_supers() that corrupts the rwsem state, triggering a DEBUG_RWSEMS warning:

[ 182.601148] sysrq: Emergency Thaw of all frozen filesystems [ 182.601865] ------------[ cut here ]------------ [ 182.602375] DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) && !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE)): count = 0x0, magic = 0xffff99b1011e5870, owner = 0x0, curr 0xffff99b101b06c80, list not empty [ 182.603817] WARNING: kernel/locking/rwsem.c:1412 at up_write+0xa3/0x170, CPU#2: kworker/2:1/53 [ 182.604578] Modules linked in: [ 182.604864] CPU: 2 UID: 0 PID: 53 Comm: kworker/2:1 Not tainted 7.2.0-rc4-00001-gbd3bd93ea98a-dirty #4 PREEMPT(lazy) [ 182.605711] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1kylin1 04/01/2014 [ 182.606417] Workqueue: events do_thaw_all [ 182.606750] RIP: 0010:up_write+0xaf/0x170 [ 182.607076] Code: 19 3a 92 48 0f 44 c2 48 8b 55 08 48 8b 55 00 4c 8b 45 08 48 8b 55 00 48 8d 3d ad 91 e0 01 48 8b 4d 20 50 48 c7 c6 f0 8c 26 92 <67> 48 0f b9 3a e8…