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Subject[PATCH 122/141] V4L/DVB (3394): Bttv: correct bttv_risc_packed buffer size
Date
From: Duncan Sands <duncan.sands@math.u-psud.fr>
Date: 1141009788 -0300

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 <baldrick@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
---

diff --git a/drivers/media/video/bttv-risc.c b/drivers/media/video/bttv-risc.c
diff --git a/drivers/media/video/bttv-risc.c b/drivers/media/video/bttv-risc.c
index b40e973..a60c211 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, struc
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, struc

/* 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, struc

/* 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, stru

/* 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
diff --git a/drivers/media/video/cx88/cx88-core.c b/drivers/media/video/cx88/cx88-core.c
index eda7cd8..25be3a9 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

/* 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

/* 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;
}

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