video: video_bmp: fix out-of-bounds write in RLE8 decoder - #944
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atkinchris wants to merge 1 commit into
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video: video_bmp: fix out-of-bounds write in RLE8 decoder#944atkinchris wants to merge 1 commit into
atkinchris wants to merge 1 commit into
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video_display_rle8_bitmap() handles the BMP RLE8 DELTA escape and EOL marker without bounds checking y before writing through the fb pointer. y starts at height-1 and decrements; a single DELTA can drive it negative. Subsequent encoded and unencoded run checks use "if (y < height)" which passes for any negative y (signed comparison), so the decoder continues writing through an underflowed fb pointer. Add bounds checks to the DELTA and EOL handlers to stop decoding when y leaves the image, and add a lower-bound check for y on both the encoded and unencoded run paths.
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Summary
video_display_rle8_bitmap()adjustyand the framebuffer pointer without bounds checkingyvalues produced by these escapesDetail
ystarts atheight - 1and decrements. The RLE8 DELTA escape (0x00 0x02 dx dy) subtractsdyfromywith no validation, and the EOL handler decrementsyunconditionally. Either can driveynegative. The existing bounds checks on encoded runs (y < height) and unencoded runs (y < height) both pass for negativeybecause the comparisons are signed, so the decoder continues writing through an underflowed framebuffer pointer.This patch adds bounds checks to the DELTA and EOL handlers to stop decoding when
ygoes negative, and adds a lower-bound check foryon both run-type code paths.The same bug exists independently in the Rockchip U-Boot fork's
drivers/video/drm/bmp_helper.c, where a fix has been submitted as rockchip-linux/u-boot#100.