4.4-stable review patch. If anyone has any objections, please let me know.
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From: NeilBrown neilb@suse.com
commit b602345da6cbb135ba68cf042df8ec9a73da7981 upstream.
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/?... Cc: stable@vger.kernel.org (v2.6.12+) Signed-off-by: NeilBrown neilb@suse.com Signed-off-by: J. Bruce Fields bfields@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/nfsd/nfs3proc.c | 16 ++++++++++++++-- fs/nfsd/nfs3xdr.c | 1 + 2 files changed, 15 insertions(+), 2 deletions(-)
--- a/fs/nfsd/nfs3proc.c +++ b/fs/nfsd/nfs3proc.c @@ -430,8 +430,19 @@ nfsd3_proc_readdir(struct svc_rqst *rqst &resp->common, nfs3svc_encode_entry); memcpy(resp->verf, argp->verf, 8); resp->count = resp->buffer - argp->buffer; - if (resp->offset) - xdr_encode_hyper(resp->offset, argp->cookie); + if (resp->offset) { + loff_t offset = argp->cookie; + + if (unlikely(resp->offset1)) { + /* we ended up with offset on a page boundary */ + *resp->offset = htonl(offset >> 32); + *resp->offset1 = htonl(offset & 0xffffffff); + resp->offset1 = NULL; + } else { + xdr_encode_hyper(resp->offset, offset); + } + resp->offset = NULL; + }
RETURN_STATUS(nfserr); } @@ -499,6 +510,7 @@ nfsd3_proc_readdirplus(struct svc_rqst * } else { xdr_encode_hyper(resp->offset, offset); } + resp->offset = NULL; }
RETURN_STATUS(nfserr); --- a/fs/nfsd/nfs3xdr.c +++ b/fs/nfsd/nfs3xdr.c @@ -898,6 +898,7 @@ encode_entry(struct readdir_cd *ccd, con } else { xdr_encode_hyper(cd->offset, offset64); } + cd->offset = NULL; }
/*