When a 9P server sends an L9P_RWALK reply, it specifies the number of qids enclosed as a 16-bit number. l9p_puqids() unpacks the specified number of qids into its qids argument, which is the wqid element of a struct l9p_f_rwalk: struct l9p_f_rwalk { struct l9p_hdr hdr; uint16_t nwqid; struct l9p_qid wqid[L9P_MAX_WELEM]; }; #define L9P_MAX_WELEM 256 l9p_puqids() doesn't check the server's number against this maximum: static ssize_t l9p_puqids(struct l9p_message *msg, uint16_t *num, struct l9p_qid *qids) { size_t i, lim; ssize_t ret, r; r = l9p_pu16(msg, num); if (r > 0) { for (i = 0, lim = *num; i < lim; i++) { ret = l9p_puqid(msg, &qids[i]); if (ret < 0) return (-1); r += ret; } } return (r); } So if a malicious or enthusiastic server sends back more than 256 qids, the client will write them beyond the end of wqid[].
A bhyve guest may be able to trigger this overflow in the bhyve host.
Jakub, do you have some time to look at this?
https://reviews.freebsd.org/D35907 I'll echo a question from the review here: does fs_walk() have a similar problem in that it doesn't validate twalk.nwname?
A commit in branch main references this bug: URL: https://cgit.FreeBSD.org/src/commit/?id=2dd83b3f0507fc7bc64b908fb88f285a3b9663c8 commit 2dd83b3f0507fc7bc64b908fb88f285a3b9663c8 Author: Konrad Sewiłło-Jopek <kjopek@gmail.com> AuthorDate: 2022-08-08 16:25:48 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2022-08-08 16:50:43 +0000 lib9p: Remove potential buffer overwrite in l9p_puqids() Structure l9p_f_wralk reserves at most L9P_MAX_WELEM entries and that number actually set the maximum we can safely use. PR: 265385 Reviewed by: markj MFC after: 1 day Differential Revision: https://reviews.freebsd.org/D35907 contrib/lib9p/pack.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-)
A commit in branch stable/13 references this bug: URL: https://cgit.FreeBSD.org/src/commit/?id=c536045c51da78a85138e963d3b7e13a547713c9 commit c536045c51da78a85138e963d3b7e13a547713c9 Author: Konrad Sewiłło-Jopek <kjopek@gmail.com> AuthorDate: 2022-08-08 16:25:48 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2022-08-09 13:33:14 +0000 lib9p: Remove potential buffer overwrite in l9p_puqids() Structure l9p_f_wralk reserves at most L9P_MAX_WELEM entries and that number actually set the maximum we can safely use. PR: 265385 Reviewed by: markj (cherry picked from commit 2dd83b3f0507fc7bc64b908fb88f285a3b9663c8) contrib/lib9p/pack.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-)
Thank you for the report.
A commit in branch releng/13.0 references this bug: URL: https://cgit.FreeBSD.org/src/commit/?id=70a2cf7bb2e0010805dde782ce7a1fe325d6f7e2 commit 70a2cf7bb2e0010805dde782ce7a1fe325d6f7e2 Author: Konrad Sewiłło-Jopek <kjopek@gmail.com> AuthorDate: 2022-08-08 16:25:48 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2022-08-09 20:00:03 +0000 lib9p: Remove potential buffer overwrite in l9p_puqids() Structure l9p_f_wralk reserves at most L9P_MAX_WELEM entries and that number actually set the maximum we can safely use. Approved by: so Security: FreeBSD-SA-22:12.lib9p PR: 265385 Reviewed by: markj (cherry picked from commit 2dd83b3f0507fc7bc64b908fb88f285a3b9663c8) (cherry picked from commit c536045c51da78a85138e963d3b7e13a547713c9) contrib/lib9p/pack.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-)
A commit in branch releng/13.1 references this bug: URL: https://cgit.FreeBSD.org/src/commit/?id=7dfe949791e764115dda17ec6b21fba2e0a86a2e commit 7dfe949791e764115dda17ec6b21fba2e0a86a2e Author: Konrad Sewiłło-Jopek <kjopek@gmail.com> AuthorDate: 2022-08-08 16:25:48 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2022-08-09 20:01:13 +0000 lib9p: Remove potential buffer overwrite in l9p_puqids() Structure l9p_f_wralk reserves at most L9P_MAX_WELEM entries and that number actually set the maximum we can safely use. Approved by: so Security: FreeBSD-SA-22:12.lib9p PR: 265385 Reviewed by: markj (cherry picked from commit 2dd83b3f0507fc7bc64b908fb88f285a3b9663c8) (cherry picked from commit c536045c51da78a85138e963d3b7e13a547713c9) contrib/lib9p/pack.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-)