[PATCH AUTOSEL 6.13 4/8] 9p/net: fix improper handling of bogus negative read/write replies

Sasha Levin
2025-04-07T18:17:09Z

From: Dominique Martinet <asmadeus@codewreck.org>

[ Upstream commit d0259a856afca31d699b706ed5e2adf11086c73b ]

In p9_client_write() and p9_client_read_once(), if the server
incorrectly replies with success but a negative write/read count then we
would consider written (negative) <= rsize (positive) because both
variables were signed.

Make variables unsigned to avoid this problem.

The reproducer linked below now fails with the following error instead
of a null pointer deref:
9pnet: bogus RWRITE count (4294967295 > 3)

Reported-by: Robert Morris <rtm@mit.edu>
Closes: https://lore.kernel.org/16271.1734448631@26-5-164.dynamic.csail.mit.edu
Message-ID: <20250319-9p_unsigned_rw-v3-1-71327f1503d0@codewreck.org>
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/9p/client.c | 30 ++++++++++++++++--------------
1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/net/9p/client.c b/net/9p/client.c
index 09f8ced9f8bb7..52a5497cfca79 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -1548,7 +1548,8 @@ p9_client_read_once(struct p9_fid *fid, u64 offset, struct iov_iter *to,
struct p9_client *clnt = fid->clnt;
struct p9_req_t *req;
int count = iov_iter_count(to);
- int rsize, received, non_zc = 0;
+ u32 rsize, received;
+ bool non_zc = false;
char *dataptr;

*err = 0;
@@ -1571,7 +1572,7 @@ p9_client_read_once(struct p9_fid *fid, u64 offset, struct iov_iter *to,
0, 11, "dqd", fid->fid,
offset, rsize);
} else {
- non_zc = 1;
+ non_zc = true;
req = p9_client_rpc(clnt, P9_TREAD, "dqd", fid->fid, offset,
rsize);
}
@@ -1592,11 +1593,11 @@ p9_client_read_once(struct p9_fid *fid, u64 offset, struct iov_iter *to,
return 0;
}
if (rsize < received) {
- pr_err("bogus RREAD count (%d > %d)\n", received, rsize);
+ pr_err("bogus RREAD count (%u > %u)\n", received, rsize);
received = rsize;
}

- p9_debug(P9_DEBUG_9P, "<<< RREAD count %d\n", received);
+ p9_debug(P9_DEBUG_9P, "<<< RREAD count %u\n", received);

if (non_zc) {
int n = copy_to_iter(dataptr, received, to);
@@ -1623,9 +1624,9 @@ p9_client_write(struct p9_fid *fid, u64 offset, struct iov_iter *from, int *err)
*err = 0;

while (iov_iter_count(from)) {
- int count = iov_iter_count(from);
- int rsize = fid->iounit;
- int written;
+ size_t count = iov_iter_count(from);
+ u32 rsize = fid->iounit;
+ u32 written;

if (!rsize || rsize > clnt->msize - P9_IOHDRSZ)
rsize = clnt->msize - P9_IOHDRSZ;
@@ -1633,7 +1634,7 @@ p9_client_write(struct p9_fid *fid, u64 offset, struct iov_iter *from, int *err)
if (count < rsize)
rsize = count;

- p9_debug(P9_DEBUG_9P, ">>> TWRITE fid %d offset %llu count %d (/%d)\n",
+ p9_debug(P9_DEBUG_9P, ">>> TWRITE fid %d offset %llu count %u (/%zu)\n",
fid->fid, offset, rsize, count);

/* Don't bother zerocopy for small IO (< 1024) */
@@ -1659,11 +1660,11 @@ p9_client_write(struct p9_fid *fid, u64 offset, struct iov_iter *from, int *err)
break;
}
if (rsize < written) {
- pr_err("bogus RWRITE count (%d > %d)\n", written, rsize);
+ pr_err("bogus RWRITE count (%u > %u)\n", written, rsize);
written = rsize;
}

- p9_debug(P9_DEBUG_9P, "<<< RWRITE count %d\n", written);
+ p9_debug(P9_DEBUG_9P, "<<< RWRITE count %u\n", written);

p9_req_put(clnt, req);
iov_iter_revert(from, count - written - iov_iter_count(from));
@@ -2098,7 +2099,8 @@ EXPORT_SYMBOL_GPL(p9_client_xattrcreate);

int p9_client_readdir(struct p9_fid *fid, char *data, u32 count, u64 offset)
{
- int err, rsize, non_zc = 0;
+ int err, non_zc = 0;
+ u32 rsize;
struct p9_client *clnt;
struct p9_req_t *req;
char *dataptr;
@@ -2107,7 +2109,7 @@ int p9_client_readdir(struct p9_fid *fid, char *data, u32 count, u64 offset)

iov_iter_kvec(&to, ITER_DEST, &kv, 1, count);

- p9_debug(P9_DEBUG_9P, ">>> TREADDIR fid %d offset %llu count %d\n",
+ p9_debug(P9_DEBUG_9P, ">>> TREADDIR fid %d offset %llu count %u\n",
fid->fid, offset, count);

clnt = fid->clnt;
@@ -2142,11 +2144,11 @@ int p9_client_readdir(struct p9_fid *fid, char *data, u32 count, u64 offset)
goto free_and_error;
}
if (rsize < count) {
- pr_err("bogus RREADDIR count (%d > %d)\n", count, rsize);
+ pr_err("bogus RREADDIR count (%u > %u)\n", count, rsize);
count = rsize;
}

- p9_debug(P9_DEBUG_9P, "<<< RREADDIR count %d\n", count);
+ p9_debug(P9_DEBUG_9P, "<<< RREADDIR count %u\n", count);

if (non_zc)
memmove(data, dataptr, count);
--
2.39.5