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TAGGED_RCPT(0.00)[55e03490a0175b8dd81d]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim,suse.de:mid] X-Spam-Level: X-Rspamd-Action: no action X-Rspamd-Queue-Id: 8FB52336A6 X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spam-Flag: NO Hi Am 18.01.26 um 14:47 schrieb Osama Abdelkader: > The function fb_pad_unaligned_buffer() was reading idx+1 bytes per row > from the source buffer, but when mod == 0 (font width is a multiple of > 8 bits), the source buffer only has idx bytes per row. This caused a > slab-out-of-bounds read when accessing src[idx] after the inner loop. > > Fix this by only reading the extra byte when mod != 0, ensuring we > never read beyond the source buffer boundaries. > > This fixes the KASAN slab-out-of-bounds read reported by syzkaller: > https://syzkaller.appspot.com/bug?extid=55e03490a0175b8dd81d > > Reported-by: syzbot+55e03490a0175b8dd81d@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=55e03490a0175b8dd81d > Signed-off-by: Osama Abdelkader > --- > drivers/video/fbdev/core/fbmem.c | 18 ++++++++++-------- > 1 file changed, 10 insertions(+), 8 deletions(-) > > diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c > index eff757ebbed1..a0c4932a6758 100644 > --- a/drivers/video/fbdev/core/fbmem.c > +++ b/drivers/video/fbdev/core/fbmem.c > @@ -113,15 +113,17 @@ void fb_pad_unaligned_buffer(u8 *dst, u32 d_pitch, u8 *src, u32 idx, u32 height, > dst[j+1] = tmp; > src++; > } > - tmp = dst[idx]; > - tmp &= mask; > - tmp |= *src >> shift_low; > - dst[idx] = tmp; > - if (shift_high < mod) { > - tmp = *src << shift_high; > - dst[idx+1] = tmp; > + if (mod) { How do we end up here if mod equals 0? When I look at the callers of this function, cases with (mod == 0) take an entirely different branch. [1] [2] Best regards Thomas [1] https://elixir.bootlin.com/linux/v6.18.6/source/drivers/video/fbdev/core/bitblit.c#L208 [2] https://elixir.bootlin.com/linux/v6.18.6/source/drivers/video/fbdev/core/fbcon_ud.c#L199 > + tmp = dst[idx]; > + tmp &= mask; > + tmp |= *src >> shift_low; > + dst[idx] = tmp; > + if (shift_high < mod) { > + tmp = *src << shift_high; > + dst[idx+1] = tmp; > + } > + src++; > } > - src++; > dst += d_pitch; > } > } -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)