path: root/lib/genalloc.c
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authorThadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>2012-10-25 13:37:51 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-10-25 14:37:52 -0700
commiteedce141cd2dad8d0cefc5468ef41898949a7031 (patch)
treee7b7c4c69114df9a830ec4c3f8e70dd4b30015ca /lib/genalloc.c
parentfd6de5300e6fcad5621ef7e78eb227de9d4c8b79 (diff)
genalloc: stop crashing the system when destroying a pool
The genalloc code uses the bitmap API from include/linux/bitmap.h and lib/bitmap.c, which is based on long values. Both bitmap_set from lib/bitmap.c and bitmap_set_ll, which is the lockless version from genalloc.c, use BITMAP_LAST_WORD_MASK to set the first bits in a long in the bitmap. That one uses (1 << bits) - 1, 0b111, if you are setting the first three bits. This means that the API counts from the least significant bits (LSB from now on) to the MSB. The LSB in the first long is bit 0, then. The same works for the lookup functions. The genalloc code uses longs for the bitmap, as it should. In include/linux/genalloc.h, struct gen_pool_chunk has unsigned long bits[0] as its last member. When allocating the struct, genalloc should reserve enough space for the bitmap. This should be a proper number of longs that can fit the amount of bits in the bitmap. However, genalloc allocates an integer number of bytes that fit the amount of bits, but may not be an integer amount of longs. 9 bytes, for example, could be allocated for 70 bits. This is a problem in itself if the Least Significat Bit in a long is in the byte with the largest address, which happens in Big Endian machines. This means genalloc is not allocating the byte in which it will try to set or check for a bit. This may end up in memory corruption, where genalloc will try to set the bits it has not allocated. In fact, genalloc may not set these bits because it may find them already set, because they were not zeroed since they were not allocated. And that's what causes a BUG when gen_pool_destroy is called and check for any set bits. What really happens is that genalloc uses kmalloc_node with __GFP_ZERO on gen_pool_add_virt. With SLAB and SLUB, this means the whole slab will be cleared, not only the requested bytes. Since struct gen_pool_chunk has a size that is a multiple of 8, and slab sizes are multiples of 8, we get lucky and allocate and clear the right amount of bytes. Hower, this is not the case with SLOB or with older code that did memset after allocating instead of using __GFP_ZERO. So, a simple module as this (running 3.6.0), will cause a crash when rmmod'ed. [root@phantom-lp2 foo]# cat foo.c #include <linux/kernel.h> #include <linux/module.h> #include <linux/init.h> #include <linux/genalloc.h> MODULE_LICENSE("GPL"); MODULE_VERSION("0.1"); static struct gen_pool *foo_pool; static __init int foo_init(void) { int ret; foo_pool = gen_pool_create(10, -1); if (!foo_pool) return -ENOMEM; ret = gen_pool_add(foo_pool, 0xa0000000, 32 << 10, -1); if (ret) { gen_pool_destroy(foo_pool); return ret; } return 0; } static __exit void foo_exit(void) { gen_pool_destroy(foo_pool); } module_init(foo_init); module_exit(foo_exit); [root@phantom-lp2 foo]# zcat /proc/config.gz | grep SLOB CONFIG_SLOB=y [root@phantom-lp2 foo]# insmod ./foo.ko [root@phantom-lp2 foo]# rmmod foo ------------[ cut here ]------------ kernel BUG at lib/genalloc.c:243! cpu 0x4: Vector: 700 (Program Check) at [c0000000bb0e7960] pc: c0000000003cb50c: .gen_pool_destroy+0xac/0x110 lr: c0000000003cb4fc: .gen_pool_destroy+0x9c/0x110 sp: c0000000bb0e7be0 msr: 8000000000029032 current = 0xc0000000bb0e0000 paca = 0xc000000006d30e00 softe: 0 irq_happened: 0x01 pid = 13044, comm = rmmod kernel BUG at lib/genalloc.c:243! [c0000000bb0e7ca0] d000000004b00020 .foo_exit+0x20/0x38 [foo] [c0000000bb0e7d20] c0000000000dff98 .SyS_delete_module+0x1a8/0x290 [c0000000bb0e7e30] c0000000000097d4 syscall_exit+0x0/0x94 --- Exception: c00 (System Call) at 000000800753d1a0 SP (fffd0b0e640) is in userspace Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Benjamin Gaignard <benjamin.gaignard@stericsson.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib/genalloc.c')
1 files changed, 1 insertions, 1 deletions
diff --git a/lib/genalloc.c b/lib/genalloc.c
index ca208a92628..54920433705 100644
--- a/lib/genalloc.c
+++ b/lib/genalloc.c
@@ -178,7 +178,7 @@ int gen_pool_add_virt(struct gen_pool *pool, unsigned long virt, phys_addr_t phy
struct gen_pool_chunk *chunk;
int nbits = size >> pool->min_alloc_order;
int nbytes = sizeof(struct gen_pool_chunk) +
- (nbits + BITS_PER_BYTE - 1) / BITS_PER_BYTE;
+ BITS_TO_LONGS(nbits) * sizeof(long);
chunk = kmalloc_node(nbytes, GFP_KERNEL | __GFP_ZERO, nid);
if (unlikely(chunk == NULL))