3.16.72-rc1 review patch. If anyone has any objections, please let me know.
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From: Denis Efremov efremov@ispras.ru
commit 5635f897ed83fd539df78e98ba69ee91592f9bb8 upstream.
This fixes a global out-of-bounds read access in the next_valid_format function of the floppy driver.
The values from autodetect field of the struct floppy_drive_params are used as indices for the floppy_type array in the next_valid_format function 'floppy_type[DP->autodetect[probed_format]].sect'.
To trigger the bug, one could use a value out of range and set the drive parameters with the FDSETDRVPRM ioctl. A floppy disk is not required to be inserted.
CAP_SYS_ADMIN is required to call FDSETDRVPRM.
The patch adds the check for values of the autodetect field to be in the '0 <= x < ARRAY_SIZE(floppy_type)' range of the floppy_type array indices.
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 [bwh: Backported to 3.16: Drop changes in compat_setdrvprm(), as compat ioctls go via fd_ioctl_locked() after translation in compat_ioctl.c.] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/drivers/block/floppy.c +++ b/drivers/block/floppy.c @@ -3383,6 +3383,20 @@ static int fd_getgeo(struct block_device return 0; }
+static bool valid_floppy_drive_params(const short autodetect[8]) +{ + size_t floppy_type_size = ARRAY_SIZE(floppy_type); + size_t i = 0; + + for (i = 0; i < 8; ++i) { + if (autodetect[i] < 0 || + autodetect[i] >= floppy_type_size) + return false; + } + + return true; +} + static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int cmd, unsigned long param) { @@ -3509,6 +3523,8 @@ static int fd_locked_ioctl(struct block_ SUPBOUND(size, strlen((const char *)outparam) + 1); break; case FDSETDRVPRM: + if (!valid_floppy_drive_params(inparam.dp.autodetect)) + return -EINVAL; *UDP = inparam.dp; break; case FDGETDRVPRM: