[PATCH] PCI: Avoid potential NULL pointer dereference in pci_scan_bridge

[PATCH] PCI: Avoid potential NULL pointer dereference in pci_scan_bridge

[Jesper Juhl]

pci_add_new_bus() calls pci_alloc_child_bus() which calls pci_alloc_bus() 
that allocates memory dynamically with kzalloc(). The return value of 
kzalloc() is the pointer that's eventually returned from 
pci_add_new_bus(), so since kzalloc() can fail and return NULL so can 
pci_add_new_bus(). Thus we may end up dereferencing a NULL pointer in 
drivers/pci/probe.c::pci_scan_bridge(). Seems to me we should test for 
this and bail out if it happens rather than crashing.
Also removed some trailing whitespace that bugged me while looking at 
this.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
---
 probe.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

  compile tested

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index c84900d..44cbbba 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -764,6 +764,8 @@ int __devinit pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max,
 		if (pci_find_bus(pci_domain_nr(bus), max+1))
 			goto out;
 		child = pci_add_new_bus(bus, dev, ++max);
+		if (!child)
+			goto out;
 		buses = (buses & 0xff000000)
 		      | ((unsigned int)(child->primary)     <<  0)
 		      | ((unsigned int)(child->secondary)   <<  8)
@@ -777,7 +779,7 @@ int __devinit pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max,
 			buses &= ~0xff000000;
 			buses |= CARDBUS_LATENCY_TIMER << 24;
 		}
-			
+
 		/*
 		 * We need to blast all three values with a single write.
 		 */


-- 
Jesper Juhl <jj@chaosbits.net>            http://www.chaosbits.net/
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please.

Re: [PATCH] PCI: Avoid potential NULL pointer dereference in pci_scan_bridge

[Jesse Barnes]

On Mon, 24 Jan 2011 21:14:33 +0100 (CET)
Jesper Juhl <jj@chaosbits.net> wrote:

> pci_add_new_bus() calls pci_alloc_child_bus() which calls pci_alloc_bus() 
> that allocates memory dynamically with kzalloc(). The return value of 
> kzalloc() is the pointer that's eventually returned from 
> pci_add_new_bus(), so since kzalloc() can fail and return NULL so can 
> pci_add_new_bus(). Thus we may end up dereferencing a NULL pointer in 
> drivers/pci/probe.c::pci_scan_bridge(). Seems to me we should test for 
> this and bail out if it happens rather than crashing.
> Also removed some trailing whitespace that bugged me while looking at 
> this.
> 
> Signed-off-by: Jesper Juhl <jj@chaosbits.net>
> ---

Applied to linux-next (in the absence of actual reports I'll be
conservative), thanks.

-- 
Jesse Barnes, Intel Open Source Technology Center