From: Denis Efremov efremov@ispras.ru
[ Upstream commit f3554aeb991214cbfafd17d55e2bfddb50282e32 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/block/floppy.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c index a8de56f1936d..b1425b218606 100644 --- a/drivers/block/floppy.c +++ b/drivers/block/floppy.c @@ -2119,6 +2119,9 @@ 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;
@@ -3243,6 +3246,8 @@ 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)