devpts: fix error handling in devpts_mntget()
If devpts_ptmx_path() returns an error code, then devpts_mntget()
dereferences an ERR_PTR():
BUG: unable to handle kernel paging request at fffffffffffffff5
IP: devpts_mntget+0x13f/0x280 fs/devpts/inode.c:173
Fix it by returning early in the error paths.
Reproducer:
#define _GNU_SOURCE
#include <fcntl.h>
#include <sched.h>
#include <sys/ioctl.h>
#define TIOCGPTPEER _IO('T', 0x41)
int main()
{
for (;;) {
int fd = open("/dev/ptmx", 0);
unshare(CLONE_NEWNS);
ioctl(fd, TIOCGPTPEER, 0);
}
}
Fixes: 311fc65c9fb9 ("pty: Repair TIOCGPTPEER")
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: <stable@vger.kernel.org> # v4.13+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 7eae33f..e31d6ed 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -168,11 +168,11 @@
dput(path.dentry);
if (err) {
mntput(path.mnt);
- path.mnt = ERR_PTR(err);
+ return ERR_PTR(err);
}
if (DEVPTS_SB(path.mnt->mnt_sb) != fsi) {
mntput(path.mnt);
- path.mnt = ERR_PTR(-ENODEV);
+ return ERR_PTR(-ENODEV);
}
return path.mnt;
}