From 522f6e6cba6880a038e2bd88e10390b84cd3febd Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Sat, 23 May 2020 16:21:55 +0300
Subject: [PATCH] ovl: fix out of bounds access warning in ovl_check_fb_len()
syzbot reported out of bounds memory access from open_by_handle_at()
with a crafted file handle that looks like this:
{ .handle_bytes = 2, .handle_type = OVL_FILEID_V1 }
handle_bytes gets rounded down to 0 and we end up calling:
ovl_check_fh_len(fh, 0) => ovl_check_fb_len(fh + 3, -3)
But fh buffer is only 2 bytes long, so accessing struct ovl_fb at
fh + 3 is illegal.
Fixes: cbe7fba8edfc ("ovl: make sure that real fid is 32bit aligned in memory")
Reported-and-tested-by: syzbot+61958888b1c60361a791@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org> # v5.5
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
fs/overlayfs/overlayfs.h | 3 +++
1 file changed, 3 insertions(+)
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 76747f5b051756..ffbb57b2d7f6b9 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -355,6 +355,9 @@ int ovl_check_fb_len(struct ovl_fb *fb, int fb_len);
static inline int ovl_check_fh_len(struct ovl_fh *fh, int fh_len)
{
+ if (fh_len < sizeof(struct ovl_fh))
+ return -EINVAL;
+
return ovl_check_fb_len(&fh->fb, fh_len - OVL_FH_WIRE_OFFSET);
}
--
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