The bounds check in do_rw() was written as:
if (cnt + blk > limit)
with cnt and blk declared as uint (unsigned int) and limit as ulong.
C's usual arithmetic conversions are applied per binary operator, so
"cnt + blk" is evaluated entirely in unsigned int and wraps modulo
2^32 before the result is widened for the comparison against limit.
With cnt = 0xFFFFFFFF and blk = 1 the sum wraps to 0 and the guard
passes, allowing blk_dread()/blk_dwrite() to be issued with a 4 GiB
transfer count that runs past the partition (or, when no partition
is selected, the entire device).
Rewrite the check as two comparisons that do not overflow:
if (blk > limit || cnt > limit - blk)
The subtraction is performed in ulong (limit's type), so no truncation
occurs, and the two sub-conditions cover both "start block past end"
and "count would push us past end" failure modes.
Signed-off-by: Naveen Kumar Chaudhary <naveen.osdev@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Naveen Kumar ChaudharyandTom Rini
1b8283bd32