From b602345da6cbb135ba68cf042df8ec9a73da7981 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Mon, 4 Mar 2019 14:08:22 +1100 Subject: nfsd: fix memory corruption caused by readdir If the result of an NFSv3 readdir{,plus} request results in the "offset" on one entry having to be split across 2 pages, and is sized so that the next directory entry doesn't fit in the requested size, then memory corruption can happen. When encode_entry() is called after encoding the last entry that fits, it notices that ->offset and ->offset1 are set, and so stores the offset value in the two pages as required. It clears ->offset1 but *does not* clear ->offset. Normally this omission doesn't matter as encode_entry_baggage() will be called, and will set ->offset to a suitable value (not on a page boundary). But in the case where cd->buflen < elen and nfserr_toosmall is returned, ->offset is not reset. This means that nfsd3proc_readdirplus will see ->offset with a value 4 bytes before the end of a page, and ->offset1 set to NULL. It will try to write 8bytes to ->offset. If we are lucky, the next page will be read-only, and the system will BUG: unable to handle kernel paging request at... If we are unlucky, some innocent page will have the first 4 bytes corrupted. nfsd3proc_readdir() doesn't even check for ->offset1, it just blindly writes 8 bytes to the offset wherever it is. Fix this by clearing ->offset after it is used, and copying the ->offset handling code from nfsd3_proc_readdirplus into nfsd3_proc_readdir. (Note that the commit hash in the Fixes tag is from the 'history' tree - this bug predates git). Fixes: 0b1d57cf7654 ("[PATCH] kNFSd: Fix nfs3 dentry encoding") Fixes-URL: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=0b1d57cf7654 Cc: stable@vger.kernel.org (v2.6.12+) Signed-off-by: NeilBrown Signed-off-by: J. Bruce Fields --- fs/nfsd/nfs3xdr.c | 1 + 1 file changed, 1 insertion(+) (limited to 'fs/nfsd/nfs3xdr.c') diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c index 9b973f4f7d01..83919116d5cb 100644 --- a/fs/nfsd/nfs3xdr.c +++ b/fs/nfsd/nfs3xdr.c @@ -921,6 +921,7 @@ encode_entry(struct readdir_cd *ccd, const char *name, int namlen, } else { xdr_encode_hyper(cd->offset, offset64); } + cd->offset = NULL; } /* -- cgit v1.2.3