From 4a287cfeea7056dc71d2bc352ae490a2a5bcceb0 Mon Sep 17 00:00:00 2001 From: Duncan Sands Date: Mon, 27 Feb 2006 00:09:48 -0300 Subject: [PATCH] V4L/DVB (3394): Bttv: correct bttv_risc_packed buffer size This patch fixes the strange crashes I was seeing after using bttv card, caused by a buffer overflow in bttv_risc_packed. The instruction buffer size calculation contains two errors: (a) a non-zero padding value can push the start of the next bpl section to just before a page border, leading to more scanline splits and thus additional instructions. (b) the first DMA region can be smaller than one page, so there can be a scanline split even if bpl*lines is smaller than PAGE_SIZE. For example, consider the case where offset is 0, bpl is 2, padding is 4094, lines is smaller than 2048, the first DMA region has size 1 and all others have size PAGE_SIZE, assumed to equal 4096. Then all bpl regions cross page borders and the number of instructions written is 2*lines+2, rather than lines+2 (the current estimate). With this patch the number of instructions for this example is estimated to be 2*lines+3. Also, the BUG_ON that was supposed to catch buffer overflows contained a thinko causing it fire only if the buffer was overrun by a factor of 16 or more, so it fixes the the BUG_ON's (using sizeof rather than "4"). Signed-off-by: Duncan Sands Signed-off-by: Mauro Carvalho Chehab --- drivers/media/video/bttv-risc.c | 12 +++++++----- drivers/media/video/cx88/cx88-core.c | 4 ++-- 2 files changed, 9 insertions(+), 7 deletions(-) diff --git a/drivers/media/video/bttv-risc.c b/drivers/media/video/bttv-risc.c index b40e9734bf08..a60c211c9e31 100644 --- a/drivers/media/video/bttv-risc.c +++ b/drivers/media/video/bttv-risc.c @@ -51,8 +51,10 @@ bttv_risc_packed(struct bttv *btv, struct btcx_riscmem *risc, int rc; /* estimate risc mem: worst case is one write per page border + - one write per scan line + sync + jump (all 2 dwords) */ - instructions = (bpl * lines) / PAGE_SIZE + lines; + one write per scan line + sync + jump (all 2 dwords). padding + can cause next bpl to start close to a page border. First DMA + region may be smaller than PAGE_SIZE */ + instructions = 1 + ((bpl + padding) * lines) / PAGE_SIZE + lines; instructions += 2; if ((rc = btcx_riscmem_alloc(btv->c.pci,risc,instructions*8)) < 0) return rc; @@ -104,7 +106,7 @@ bttv_risc_packed(struct bttv *btv, struct btcx_riscmem *risc, /* save pointer to jmp instruction address */ risc->jmp = rp; - BUG_ON((risc->jmp - risc->cpu + 2) / 4 > risc->size); + BUG_ON((risc->jmp - risc->cpu + 2) * sizeof(*risc->cpu) > risc->size); return 0; } @@ -222,7 +224,7 @@ bttv_risc_planar(struct bttv *btv, struct btcx_riscmem *risc, /* save pointer to jmp instruction address */ risc->jmp = rp; - BUG_ON((risc->jmp - risc->cpu + 2) / 4 > risc->size); + BUG_ON((risc->jmp - risc->cpu + 2) * sizeof(*risc->cpu) > risc->size); return 0; } @@ -307,7 +309,7 @@ bttv_risc_overlay(struct bttv *btv, struct btcx_riscmem *risc, /* save pointer to jmp instruction address */ risc->jmp = rp; - BUG_ON((risc->jmp - risc->cpu + 2) / 4 > risc->size); + BUG_ON((risc->jmp - risc->cpu + 2) * sizeof(*risc->cpu) > risc->size); kfree(skips); return 0; } diff --git a/drivers/media/video/cx88/cx88-core.c b/drivers/media/video/cx88/cx88-core.c index eda7cd8b2d4a..25be3a976d09 100644 --- a/drivers/media/video/cx88/cx88-core.c +++ b/drivers/media/video/cx88/cx88-core.c @@ -163,7 +163,7 @@ int cx88_risc_buffer(struct pci_dev *pci, struct btcx_riscmem *risc, /* save pointer to jmp instruction address */ risc->jmp = rp; - BUG_ON((risc->jmp - risc->cpu + 2) / 4 > risc->size); + BUG_ON((risc->jmp - risc->cpu + 2) * sizeof (*risc->cpu) > risc->size); return 0; } @@ -188,7 +188,7 @@ int cx88_risc_databuffer(struct pci_dev *pci, struct btcx_riscmem *risc, /* save pointer to jmp instruction address */ risc->jmp = rp; - BUG_ON((risc->jmp - risc->cpu + 2) / 4 > risc->size); + BUG_ON((risc->jmp - risc->cpu + 2) * sizeof (*risc->cpu) > risc->size); return 0; } -- 2.20.1