From: Jakub Acs <acsjakub@amazon.de> mainline inclusion from mainline-v6.18 commit a7c4bb43bfdc2b9f06ee9d036028ed13a83df42a category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/ID2VH3 CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- Calling intotify_show_fdinfo() on fd watching an overlayfs inode, while the overlayfs is being unmounted, can lead to dereferencing NULL ptr. This issue was found by syzkaller. Race Condition Diagram: Thread 1 Thread 2 -------- -------- generic_shutdown_super() shrink_dcache_for_umount sb->s_root = NULL | | vfs_read() | inotify_fdinfo() | * inode get from mark * | show_mark_fhandle(m, inode) | exportfs_encode_fid(inode, ..) | ovl_encode_fh(inode, ..) | ovl_check_encode_origin(inode) | * deref i_sb->s_root * | | v fsnotify_sb_delete(sb) Which then leads to: [ 32.133461] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI [ 32.134438] KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037] [ 32.135032] CPU: 1 UID: 0 PID: 4468 Comm: systemd-coredum Not tainted 6.17.0-rc6 #22 PREEMPT(none) <snip registers, unreliable trace> [ 32.143353] Call Trace: [ 32.143732] ovl_encode_fh+0xd5/0x170 [ 32.144031] exportfs_encode_inode_fh+0x12f/0x300 [ 32.144425] show_mark_fhandle+0xbe/0x1f0 [ 32.145805] inotify_fdinfo+0x226/0x2d0 [ 32.146442] inotify_show_fdinfo+0x1c5/0x350 [ 32.147168] seq_show+0x530/0x6f0 [ 32.147449] seq_read_iter+0x503/0x12a0 [ 32.148419] seq_read+0x31f/0x410 [ 32.150714] vfs_read+0x1f0/0x9e0 [ 32.152297] ksys_read+0x125/0x240 IOW ovl_check_encode_origin derefs inode->i_sb->s_root, after it was set to NULL in the unmount path. Fix it by protecting calling exportfs_encode_fid() from show_mark_fhandle() with s_umount lock. This form of fix was suggested by Amir in [1]. [1]: https://lore.kernel.org/all/CAOQ4uxhbDwhb+2Brs1UdkoF0a3NSdBAOQPNfEHjahrgoKJp... Fixes: c45beebfde34 ("ovl: support encoding fid from inode with no alias") Signed-off-by: Jakub Acs <acsjakub@amazon.de> Cc: Jan Kara <jack@suse.cz> Cc: Amir Goldstein <amir73il@gmail.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Christian Brauner <brauner@kernel.org> Cc: linux-unionfs@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Jan Kara <jack@suse.cz> Conflicts: fs/notify/fdinfo.c [Conflicts with mainline commit 4d69c58ef2e4 ("fsnotify: Avoid -Wflex-array-member-not-at-end warning").] Signed-off-by: Wang Zhaolong <wangzhaolong@huaweicloud.com> --- fs/notify/fdinfo.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/notify/fdinfo.c b/fs/notify/fdinfo.c index 26655572975d..1aa7de55094c 100644 --- a/fs/notify/fdinfo.c +++ b/fs/notify/fdinfo.c @@ -15,10 +15,11 @@ #include "inotify/inotify.h" #include "fanotify/fanotify.h" #include "fdinfo.h" #include "fsnotify.h" +#include "../internal.h" #if defined(CONFIG_PROC_FS) #if defined(CONFIG_INOTIFY_USER) || defined(CONFIG_FANOTIFY) @@ -48,11 +49,16 @@ static void show_mark_fhandle(struct seq_file *m, struct inode *inode) int size, ret, i; f.handle.handle_bytes = sizeof(f.pad); size = f.handle.handle_bytes >> 2; + if (!super_trylock_shared(inode->i_sb)) + return; + ret = exportfs_encode_fid(inode, (struct fid *)f.handle.f_handle, &size); + up_read(&inode->i_sb->s_umount); + if ((ret == FILEID_INVALID) || (ret < 0)) return; f.handle.handle_type = ret; f.handle.handle_bytes = size * sizeof(u32); -- 2.34.3