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Date:   Wed, 19 Aug 2020 20:02:19 -0400
From:   Sasha Levin <>
Cc:     Zhe Li <>, Hou Tao <>,
        Richard Weinberger <>,
        Sasha Levin <>,
Subject: [PATCH AUTOSEL 5.4 12/22] jffs2: fix UAF problem

From: Zhe Li <>

[ Upstream commit 798b7347e4f29553db4b996393caf12f5b233daf ]

The log of UAF problem is listed below.
BUG: KASAN: use-after-free in jffs2_rmdir+0xa4/0x1cc [jffs2] at addr c1f165fc
Read of size 4 by task rm/8283
BUG kmalloc-32 (Tainted: P    B      O   ): kasan: bad access detected

INFO: Allocated in 0xbbbbbbbb age=3054364 cpu=0 pid=0
        jffs2_write_dirent+0x11c/0x9c8 [jffs2]
        jffs2_write_dirent+0x11c/0x9c8 [jffs2]
        jffs2_do_unlink+0x328/0x5fc [jffs2]
        jffs2_rmdir+0x110/0x1cc [jffs2]
INFO: Freed in 0x205b age=3054364 cpu=0 pid=0
        jffs2_add_fd_to_list+0x138/0x1dc [jffs2]
        jffs2_add_fd_to_list+0x138/0x1dc [jffs2]
        jffs2_garbage_collect_dirent.isra.3+0x21c/0x288 [jffs2]
        jffs2_garbage_collect_live+0x16bc/0x1800 [jffs2]
        jffs2_garbage_collect_pass+0x678/0x11d4 [jffs2]
        jffs2_garbage_collect_thread+0x1e8/0x3b0 [jffs2]
Call Trace:
[c17ddd20] [c02452d4] kasan_report.part.0+0x298/0x72c (unreliable)
[c17ddda0] [d2509680] jffs2_rmdir+0xa4/0x1cc [jffs2]
[c17dddd0] [c026da04] vfs_rmdir+0x180/0x268
[c17dde00] [c026f4e4] do_rmdir+0x2cc/0x300
[c17ddf40] [c001a658] ret_from_syscall+0x0/0x3c

The root cause is that we don't get "jffs2_inode_info.sem" before
we scan list "jffs2_inode_info.dents" in function jffs2_rmdir.
This patch add codes to get "jffs2_inode_info.sem" before we scan
"jffs2_inode_info.dents" to slove the UAF problem.

Signed-off-by: Zhe Li <>
Reviewed-by: Hou Tao <>
Signed-off-by: Richard Weinberger <>
Signed-off-by: Sasha Levin <>
 fs/jffs2/dir.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/jffs2/dir.c b/fs/jffs2/dir.c
index f20cff1194bb6..776493713153f 100644
--- a/fs/jffs2/dir.c
+++ b/fs/jffs2/dir.c
@@ -590,10 +590,14 @@ static int jffs2_rmdir (struct inode *dir_i, struct dentry *dentry)
 	int ret;
 	uint32_t now = JFFS2_NOW();
+	mutex_lock(&f->sem);
 	for (fd = f->dents ; fd; fd = fd->next) {
-		if (fd->ino)
+		if (fd->ino) {
+			mutex_unlock(&f->sem);
 			return -ENOTEMPTY;
+		}
+	mutex_unlock(&f->sem);
 	ret = jffs2_do_unlink(c, dir_f, dentry->,
 			      dentry->d_name.len, f, now);

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