[PATCH] libceph: validate OSD extent maps before cursor advance

[Michael Bommarito <michael.bommarito@gmail.com>]

net/ceph/osd_client.c:osd_sparse_read() validates that the sparse-read
data length matches the summed extent lengths, but it does not validate
that each OSD-supplied extent is monotonic and lies inside the original
request range. A malformed authenticated OSD reply can advertise a
far-forward nonzero extent offset with a matching data length and make
the client advance the message-data cursor beyond the request buffer.
This reaches the BUG_ON(!*length) assertion in ceph_msg_data_next() from
the client receive path.

Impact: A malicious or compromised authenticated Ceph OSD peer can crash
a kernel Ceph client via a malformed sparse-read reply.

Reject sparse extent maps that overflow, move backwards, overlap, or
extend outside the original sparse-read request before advancing the
cursor.

Fixes: f628d7999727 ("libceph: add sparse read support to OSD client")
Cc: stable@vger.kernel.org
Assisted-by: Codex:gpt-5-5-xhigh
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---

I reproduced this with a same-translation-unit KUnit test on
f5459048c38a, x86_64 with panic_on_oops=1. Without the patch, the
malformed extent triggers kernel BUG at net/ceph/messenger.c:1117 after
the benign in-range control passes. With the patch, the malformed map
returns -EREMOTEIO and both KUnit cases pass; net/ceph/osd_client.o
builds cleanly with W=1.
 net/ceph/osd_client.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
index 2ff00070c1810..76ba3abdad9b1 100644
--- a/net/ceph/osd_client.c
+++ b/net/ceph/osd_client.c
@@ -6,6 +6,7 @@
 #include <linux/err.h>
 #include <linux/highmem.h>
 #include <linux/mm.h>
+#include <linux/overflow.h>
 #include <linux/pagemap.h>
 #include <linux/slab.h>
 #include <linux/uaccess.h>
@@ -5799,6 +5800,31 @@ static inline void convert_extent_map(struct ceph_sparse_read *sr)
 }
 #endif
 
+static bool sparse_extent_map_valid(struct ceph_sparse_read *sr)
+{
+	u64 req_end, pos;
+	int i;
+
+	if (check_add_overflow(sr->sr_req_off, sr->sr_req_len, &req_end))
+		return false;
+
+	pos = sr->sr_req_off;
+	for (i = 0; i < sr->sr_count; i++) {
+		struct ceph_sparse_extent *ext = &sr->sr_extent[i];
+		u64 end;
+
+		if (ext->off < pos)
+			return false;
+		if (check_add_overflow(ext->off, ext->len, &end))
+			return false;
+		if (end > req_end)
+			return false;
+		pos = end;
+	}
+
+	return true;
+}
+
 static int osd_sparse_read(struct ceph_connection *con,
 			   struct ceph_msg_data_cursor *cursor,
 			   char **pbuf)
@@ -5856,6 +5882,10 @@ static int osd_sparse_read(struct ceph_connection *con,
 	case CEPH_SPARSE_READ_DATA_PRE:
 		/* Convert sr_datalen to host-endian */
 		sr->sr_datalen = le32_to_cpu((__force __le32)sr->sr_datalen);
+		if (!sparse_extent_map_valid(sr)) {
+			pr_warn_ratelimited("invalid sparse extent map\n");
+			return -EREMOTEIO;
+		}
 		for (i = 0; i < count; i++)
 			len += sr->sr_extent[i].len;
 		if (sr->sr_datalen != len) {