MFC r320123:

  Fix a potential sleep while holding a mutex in the sa(4) driver.

  If the user issues a MTIOCEXTGET ioctl, and the tape drive in question has
  a serial number that is longer than 80 characters, we malloc a buffer in
  saextget() to hold the output of cam_strvis().

  Since a mutex is held in that codepath, doing a M_WAITOK malloc could lead
  to sleeping while holding a mutex.  Change it to a M_NOWAIT malloc and bail
  out if we fail to allocate the memory.  Devices with serial numbers longer
  than 80 bytes are very rare (I don't recall seeing one), so this
  should be a very unusual case to hit.  But it is a bug that should be fixed.

  sys/cam/scsi/scsi_sa.c:
  	In saextget(), if we need to malloc a buffer to hold the output of
  	cam_strvis(), don't wait for the memory.  Fail and return an error
  	if we can't allocate the memory immediately.

PR:		kern/220094
Submitted by:	Jia-Ju Bai <baijiaju1990@163.com>
Sponsored by:	Spectra Logic

1 files changed, 12 insertions, 1 deletions

diff --git a/sys/cam/scsi/scsi_sa.c b/sys/cam/scsi/scsi_sa.c
index 354ff13..83c670f 100644
--- a/sys/cam/scsi/scsi_sa.c
+++ b/sys/cam/scsi/scsi_sa.c
@@ -4464,7 +4464,18 @@ saextget(struct cdev *dev, struct cam_periph *periph, struct sbuf *sb,
 		if (cgd.serial_num_len > sizeof(tmpstr)) {
 			ts2_len = cgd.serial_num_len + 1;
 			ts2_malloc = 1;
-			tmpstr2 = malloc(ts2_len, M_SCSISA, M_WAITOK | M_ZERO);
+			tmpstr2 = malloc(ts2_len, M_SCSISA, M_NOWAIT | M_ZERO);
+			/*
+			 * The 80 characters allocated on the stack above
+			 * will handle the vast majority of serial numbers.
+			 * If we run into one that is larger than that, and
+			 * we can't malloc the length without blocking,
+			 * bail out with an out of memory error.
+			 */
+			if (tmpstr2 == NULL) {
+				error = ENOMEM;
+				goto extget_bailout;
+			}
 		} else {
 			ts2_len = sizeof(tmpstr);
 			ts2_malloc = 0;