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authorDenis Efremov <efremov@ispras.ru>2019-07-12 21:55:20 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2019-07-17 14:45:49 -0700
commitf3554aeb991214cbfafd17d55e2bfddb50282e32 (patch)
tree9c8f08c1c6ce8a52f8bdb047adeba7d4024ea44c
parent0ecfebd2b52404ae0c54a878c872bb93363ada36 (diff)
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floppy: fix div-by-zero in setup_format_params
This fixes a divide by zero error in the setup_format_params function of the floppy driver. Two consecutive ioctls can trigger the bug: The first one should set the drive geometry with such .sect and .rate values for the F_SECT_PER_TRACK to become zero. Next, the floppy format operation should be called. A floppy disk is not required to be inserted. An unprivileged user could trigger the bug if the device is accessible. The patch checks F_SECT_PER_TRACK for a non-zero value in the set_geometry function. The proper check should involve a reasonable upper limit for the .sect and .rate fields, but it could change the UAPI. The patch also checks F_SECT_PER_TRACK in the setup_format_params, and cancels the formatting operation in case of zero. The bug was found by syzkaller. Signed-off-by: Denis Efremov <efremov@ispras.ru> Tested-by: Willy Tarreau <w@1wt.eu> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--drivers/block/floppy.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 9fb9b312ab6b..51246bc9709a 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -2120,6 +2120,9 @@ static void setup_format_params(int track)
raw_cmd->kernel_data = floppy_track_buffer;
raw_cmd->length = 4 * F_SECT_PER_TRACK;
+ if (!F_SECT_PER_TRACK)
+ return;
+
/* allow for about 30ms for data transport per track */
head_shift = (F_SECT_PER_TRACK + 5) / 6;
@@ -3232,6 +3235,8 @@ static int set_geometry(unsigned int cmd, struct floppy_struct *g,
/* sanity checking for parameters. */
if (g->sect <= 0 ||
g->head <= 0 ||
+ /* check for zero in F_SECT_PER_TRACK */
+ (unsigned char)((g->sect << 2) >> FD_SIZECODE(g)) == 0 ||
g->track <= 0 || g->track > UDP->tracks >> STRETCH(g) ||
/* check if reserved bits are set */
(g->stretch & ~(FD_STRETCH | FD_SWAPSIDES | FD_SECTBASEMASK)) != 0)