[PATCH] scsi: sg: clean up request on error paths in sg_read()

[Hui Peng <benquike@gmail.com>]

In sg_read(), once sg_get_rq_mark() locates a completed Sg_request and
transitions srp->done from 1 to 2, an allocation failure in kzalloc() or
a user-copy fault (-EFAULT) in copy_to_user() / sg_read_oxfer() returns
or jumps to free_old_hdr without calling sg_finish_rem_req(srp) and
sg_remove_request(sfp, srp).

Because srp->done is already 2, subsequent sg_read() calls skip the
request, permanently leaking srp->bio and keeping sfp->res_in_use = 1
(blocking SG_SET_RESERVED_SIZE with -EBUSY and wedging non-SG_FLAG_NO_DXFER
writes with -EDOM) until the file descriptor is closed.

Always call sg_finish_rem_req(srp) and sg_remove_request(sfp, srp) under
the free_old_hdr cleanup label, matching sg_new_read().

Fixes: cb59e8408381 ("[PATCH] sg.c: update")
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
---
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -480,8 +480,10 @@ sg_read(struct file *filp, char __user *buf, size_t count, loff_t * ppos)
 
 	hp = &srp->header;
 	old_hdr = kzalloc(SZ_SG_HEADER, GFP_KERNEL);
-	if (!old_hdr)
-		return -ENOMEM;
+	if (!old_hdr) {
+		retval = -ENOMEM;
+		goto free_old_hdr;
+	}
 
 	old_hdr->reply_len = (int) hp->timeout;
 	old_hdr->pack_len = old_hdr->reply_len; /* old, strange behaviour */
@@ -543,10 +545,10 @@ sg_read(struct file *filp, char __user *buf, size_t count, loff_t * ppos)
 		}
 	} else
 		count = (old_hdr->result == 0) ? 0 : -EIO;
-	sg_finish_rem_req(srp);
-	sg_remove_request(sfp, srp);
 	retval = count;
 free_old_hdr:
+	sg_finish_rem_req(srp);
+	sg_remove_request(sfp, srp);
 	kfree(old_hdr);
 	return retval;
 }
-- 
2.43.0