Commit 7f40b346462f for kernel

commit 7f40b346462f563a0d6e841a77b5163d2a882a04
Author: Stefan Haberland <sth@linux.ibm.com>
Date:   Mon Jul 27 16:28:40 2026 +0200

    s390/dasd: Fix undersized format-check buffer

    fmt_buffer_size in dasd_eckd_check_device_format() is declared as
    int, even though one of the multiplicands, sizeof(struct eckd_count),
    is a size_t. The expression

        trkcount * rpt_max * sizeof(struct eckd_count)

    is therefore correctly evaluated at 64-bit width, but the result is
    silently truncated when it is stored back into the 32-bit
    fmt_buffer_size variable. For a sufficiently large track range
    (start_unit/stop_unit are caller-controlled) this truncation
    yields a buffer size far smaller than the number of tracks actually
    requested. kzalloc() then succeeds with an undersized allocation,
    while the subsequent channel program build still operates on the
    untruncated track count and writes past the end of that buffer.

    Compute the buffer size with check_mul_overflow() and keep it in a
    size_t, so that a value that no longer fits results in -EINVAL
    instead of a silently truncated allocation size.

    Fixes: 8fd575200db5 ("s390/dasd: Add new ioctl BIODASDCHECKFMT")
    Cc: stable@vger.kernel.org #4.7
    Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
    Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
    Link: https://patch.msgid.link/20260727142840.567286-4-sth@linux.ibm.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/s390/block/dasd_eckd.c b/drivers/s390/block/dasd_eckd.c
index 74fe73b5738a..d356a9f8f016 100644
--- a/drivers/s390/block/dasd_eckd.c
+++ b/drivers/s390/block/dasd_eckd.c
@@ -20,6 +20,7 @@
 #include <linux/seq_file.h>
 #include <linux/uaccess.h>
 #include <linux/io.h>
+#include <linux/overflow.h>

 #include <asm/css_chars.h>
 #include <asm/machine.h>
@@ -3475,11 +3476,11 @@ static int dasd_eckd_check_device_format(struct dasd_device *base,
 {
 	struct dasd_eckd_private *private = base->private;
 	struct eckd_count *fmt_buffer;
-	struct irb irb;
+	size_t fmt_buffer_size;
+	unsigned int trkcount;
 	int rpt_max, rpt_exp;
-	int fmt_buffer_size;
+	struct irb irb;
 	int trk_per_cyl;
-	int trkcount;
 	int tpm = 0;
 	int rc;

@@ -3490,7 +3491,9 @@ static int dasd_eckd_check_device_format(struct dasd_device *base,
 	rpt_exp = recs_per_track(&private->rdc_data, 0, cdata->expect.blksize);

 	trkcount = cdata->expect.stop_unit - cdata->expect.start_unit + 1;
-	fmt_buffer_size = trkcount * rpt_max * sizeof(struct eckd_count);
+	if (check_mul_overflow(trkcount, rpt_max, &fmt_buffer_size) ||
+	    check_mul_overflow(fmt_buffer_size, sizeof(struct eckd_count), &fmt_buffer_size))
+		return -EINVAL;

 	fmt_buffer = kzalloc(fmt_buffer_size, GFP_KERNEL | GFP_DMA);
 	if (!fmt_buffer)