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authorNeilBrown <neilb@suse.com>2019-03-04 06:08:22 +0300
committerJ. Bruce Fields <bfields@redhat.com>2019-03-06 00:41:33 +0300
commitb602345da6cbb135ba68cf042df8ec9a73da7981 (patch)
treef557312934ce99b6fb59de6852c4f1dc221d9aba /fs/nfsd
parentc54f24e338ed2a35218f117a4a1afb5f9e2b4e64 (diff)
downloadlinux-b602345da6cbb135ba68cf042df8ec9a73da7981.tar.xz
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 <neilb@suse.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Diffstat (limited to 'fs/nfsd')
-rw-r--r--fs/nfsd/nfs3proc.c16
-rw-r--r--fs/nfsd/nfs3xdr.c1
2 files changed, 15 insertions, 2 deletions
diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 9eb8086ea841..c9cf46e0c040 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -463,8 +463,19 @@ nfsd3_proc_readdir(struct svc_rqst *rqstp)
&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);
}
@@ -533,6 +544,7 @@ nfsd3_proc_readdirplus(struct svc_rqst *rqstp)
} else {
xdr_encode_hyper(resp->offset, offset);
}
+ resp->offset = NULL;
}
RETURN_STATUS(nfserr);
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;
}
/*