3.16.83-rc1 review patch. If anyone has any objections, please let me know.
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From: Linus Torvalds torvalds@linux-foundation.org
commit 2e90ca68b0d2f5548804f22f0dd61145516171e3 upstream.
Jordy Zomer reported a KASAN out-of-bounds read in the floppy driver in wait_til_ready().
Which on the face of it can't happen, since as Willy Tarreau points out, the function does no particular memory access. Except through the FDCS macro, which just indexes a static allocation through teh current fdc, which is always checked against N_FDC.
Except the checking happens after we've already assigned the value.
The floppy driver is a disgrace (a lot of it going back to my original horrd "design"), and has no real maintainer. Nobody has the hardware, and nobody really cares. But it still gets used in virtual environment because it's one of those things that everybody supports.
The whole thing should be re-written, or at least parts of it should be seriously cleaned up. The 'current fdc' index, which is used by the FDCS macro, and which is often shadowed by a local 'fdc' variable, is a prime example of how not to write code.
But because nobody has the hardware or the motivation, let's just fix up the immediate problem with a nasty band-aid: test the fdc index before actually assigning it to the static 'fdc' variable.
Reported-by: Jordy Zomer jordy@simplyhacker.com Cc: Willy Tarreau w@1wt.eu Cc: Dan Carpenter dan.carpenter@oracle.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/block/floppy.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
--- a/drivers/block/floppy.c +++ b/drivers/block/floppy.c @@ -847,14 +847,17 @@ static void reset_fdc_info(int mode) /* selects the fdc and drive, and enables the fdc's input/dma. */ static void set_fdc(int drive) { + unsigned int new_fdc = fdc; + if (drive >= 0 && drive < N_DRIVE) { - fdc = FDC(drive); + new_fdc = FDC(drive); current_drive = drive; } - if (fdc != 1 && fdc != 0) { + if (new_fdc >= N_FDC) { pr_info("bad fdc value\n"); return; } + fdc = new_fdc; set_dor(fdc, ~0, 8); #if N_FDC > 1 set_dor(1 - fdc, ~8, 0);