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ovl: potential crash in ovl_fid_to_fh()

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The "buflen" value comes from the user and there is a potential that it
could be zero.  In do_handle_to_path() we know that "handle->handle_bytes"
is non-zero and we do:

	handle_dwords = handle->handle_bytes >> 2;

So values 1-3 become zero.  Then in ovl_fh_to_dentry() we do:

	int len = fh_len << 2;

So now len is in the "0,4-128" range and a multiple of 4.  But if
"buflen" is zero it will try to copy negative bytes when we do the
memcpy in ovl_fid_to_fh().

	memcpy(&fh->fb, fid, buflen - OVL_FH_WIRE_OFFSET);

And that will lead to a crash.  Thanks to Amir Goldstein for his help
with this patch.

Fixes: cbe7fba8ed ("ovl: make sure that real fid is 32bit aligned in memory")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Cc: <stable@vger.kernel.org> # v5.5
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Dan Carpenter 2020-05-05 21:33:31 +03:00 committed by Miklos Szeredi
parent 15fd2ea9f4
commit 9aafc1b018
1 changed files with 3 additions and 0 deletions
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3
fs/overlayfs/export.c
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@ -783,6 +783,9 @@ static struct ovl_fh *ovl_fid_to_fh(struct fid *fid, int buflen, int fh_type)
if (fh_type != OVL_FILEID_V0)
return ERR_PTR(-EINVAL);
if (buflen <= OVL_FH_WIRE_OFFSET)
return ERR_PTR(-EINVAL);
fh = kzalloc(buflen, GFP_KERNEL);
if (!fh)
return ERR_PTR(-ENOMEM);