From 190644e180794208bc638179f4d5940fe419bf9c Mon Sep 17 00:00:00 2001 From: Jesper Juhl Date: Sat, 21 Jul 2007 17:39:11 +0200 Subject: [PATCH] Fix "use after free" / "double free" bug in ati_create_gatt_pages / ati_free_gatt_pages Hi, Coverity spotted a "use after free" bug in drivers/char/agp/ati-agp.c::ati_create_gatt_pages(). The same one that was in drivers/char/agp/amd-k7-agp.c::amd_create_gatt_pages() The problem is this: If "entry = kzalloc(sizeof(struct ati_page_map), GFP_KERNEL);" fails, then there's a loop in the function to free all entries allocated so far and break out of the allocation loop. That in itself is pretty sane, but then the (now freed) 'tables' is assigned to ati_generic_private.gatt_pages and 'retval' is set to -ENOMEM which causes ati_free_gatt_pages(); to be called at the end of the function. The problem with this is that ati_free_gatt_pages() will then loop 'ati_generic_private.num_tables' times and try to free each entry in tables[] - this is bad since tables has already been freed and furthermore it will call kfree(tables) at the end - a double free. This patch removes the freeing loop in ati_create_gatt_pages() and instead relies entirely on the call to ati_free_gatt_pages() to free everything we allocated in case of an error. It also sets ati_generic_private.num_tables to the actual number of entries allocated instead of just using the value passed in from the caller - this ensures that ati_free_gatt_pages() will only attempt to free stuff that was actually allocated. Note: I'm in no way intimate with this code and I have no way to actually test this patch (besides compile test it), so while I've tried to be careful in reading the code and make sure the patch does the right thing an ACK from someone who actually knows the code in-depth would be very much appreciated. Signed-off-by: Jesper Juhl Signed-off-by: Dave Airlie --- drivers/char/agp/ati-agp.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) diff --git a/drivers/char/agp/ati-agp.c b/drivers/char/agp/ati-agp.c index 780e59e588ad..da7513d7b4e7 100644 --- a/drivers/char/agp/ati-agp.c +++ b/drivers/char/agp/ati-agp.c @@ -123,21 +123,16 @@ static int ati_create_gatt_pages(int nr_tables) for (i = 0; i < nr_tables; i++) { entry = kzalloc(sizeof(struct ati_page_map), GFP_KERNEL); + tables[i] = entry; if (entry == NULL) { - while (i > 0) { - kfree(tables[i-1]); - i--; - } - kfree(tables); retval = -ENOMEM; break; } - tables[i] = entry; retval = ati_create_page_map(entry); if (retval != 0) break; } - ati_generic_private.num_tables = nr_tables; + ati_generic_private.num_tables = i; ati_generic_private.gatt_pages = tables; if (retval != 0) -- GitLab