[PATCH] vhost-scsi: Prevent OOM from invalid protection SGL count

[Jia Jia <physicalmtea@gmail.com>]

The protection SGL path passes the result of vhost_scsi_calc_sgls()
directly to sg_alloc_table_chained(). The helper returns a negative
errno when the iterator is invalid or the request exceeds the segment
limit. The negative errno is then treated as a very large unsigned count
and sends the request into the SGL allocation path with an invalid size.

Repeated malformed T10-PI submissions from a host-side application caused
memory usage to rise sharply. MemAvailable fell to about 200 MB, and PSI
full avg10 reached about 1.46. The OOM killer terminated several userspace
processes before the endpoint cleanup completed. The kernel log included:

    [17036.451028] Out of memory: Killed process 2345 (systemd)
    [17036.493325] Out of memory: Killed process 2349 (sd-pam)
    [17078.265127] Out of memory: Killed process 1793 (networkd-dispat)

Return the calculation error before setting up the protection SGL. This
keeps the protection path consistent with the data SGL path and prevents
the invalid count from entering the allocation path.

Fixes: bca939d5bcd0 ("vhost-scsi: Dynamically allocate scatterlists")
Cc: stable@vger.kernel.org
Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
 drivers/vhost/scsi.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 9a1253b9d..8486652fd 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -972,6 +972,9 @@ vhost_scsi_mapal(struct vhost_scsi *vs, struct vhost_scsi_cmd *cmd,
 	if (prot_bytes) {
 		sgl_count = vhost_scsi_calc_sgls(prot_iter, prot_bytes,
 						 VHOST_SCSI_PREALLOC_PROT_SGLS);
+		if (sgl_count < 0)
+			return sgl_count;
+
 		cmd->prot_table.sgl = cmd->prot_sgl;
 		ret = sg_alloc_table_chained(&cmd->prot_table, sgl_count,
 					     cmd->prot_table.sgl,
-- 
2.43.0