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Commit 4a287cfe authored by Duncan Sands's avatar Duncan Sands Committed by Mauro Carvalho Chehab
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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: default avatarDuncan Sands <baldrick@free.fr>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@infradead.org>
parent 6457af5f

drivers/media/video/bttv-risc.c

+7 −5
Original line number Diff line number Diff line
@@ -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;

}

drivers/media/video/cx88/cx88-core.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

}