Messages in this thread Patch in this message | | | Date | Thu, 20 Jan 2011 13:26:59 +0100 | From | Steffen Klassert <> | Subject | flex_array related problems on selinux policy loading |
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Some recent changes to use flex_array_alloc on selinux policy loading made me unable load my selinux policy. I'm not using 'common' and 'bool' in the policy, this leads to some zero size allocations in policydb_index(). Unfortunately the behaviour on zero size allocations of flex_array_alloc() is not the same as of kmalloc(). While zero size allocations are legal on kmalloc(), flex_array_prealloc() fails with -ENOSPC if total_nr_elements is zero (this happens if I try to load my policy) or it hits a division by zero if element_size is zero.
The patch below changes the flex_array_alloc behaviour on zero size allocations to be the same as with kmalloc. I'm able to load my policy with the patch and everything seems to work fine. However, flex_array_get() returns now NULL if the pointer to the struct flex_array is a ZERO_SIZE_PTR. There is a lot of BUG_ON() in the policy handling code if flex_array_get() returns NULL, so somebody with a deeper knowledge on selinux policy handling should look into this to see if furter changes are necessary.
Steffen
Subject: [PATCH] flex_array: Change behaviour on zero size allocations
flex_array_alloc allocates the basic struct flex_array regardless whether total_nr_elements or element_size is zero. Then flex_array_prealloc fails with -ENOSPC if total_nr_elements is zero or it hits a division by zero if element_size is zero.
This patch changes the behaviour on zero size allocations to the same as kmalloc, we return ZERO_SIZE_PTR in this case. All flex_array handlers test for ZERO_SIZE_PTR and return an appropriate value to the caller.
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com> --- lib/flex_array.c | 27 +++++++++++++++++++++++++-- 1 files changed, 25 insertions(+), 2 deletions(-)
diff --git a/lib/flex_array.c b/lib/flex_array.c index c0ea40b..420d11d 100644 --- a/lib/flex_array.c +++ b/lib/flex_array.c @@ -88,8 +88,13 @@ struct flex_array *flex_array_alloc(int element_size, unsigned int total, gfp_t flags) { struct flex_array *ret; - int max_size = FLEX_ARRAY_NR_BASE_PTRS * - FLEX_ARRAY_ELEMENTS_PER_PART(element_size); + int max_size; + + if (unlikely(!element_size || !total)) + return ZERO_SIZE_PTR; + + max_size = FLEX_ARRAY_NR_BASE_PTRS * + FLEX_ARRAY_ELEMENTS_PER_PART(element_size); /* max_size will end up 0 if element_size > PAGE_SIZE */ if (total > max_size) @@ -123,6 +128,9 @@ void flex_array_free_parts(struct flex_array *fa) { int part_nr; + if (unlikely(ZERO_OR_NULL_PTR(fa))) + return; + if (elements_fit_in_base(fa)) return; for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) @@ -187,6 +195,9 @@ int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src, struct flex_array_part *part; void *dst; + if (unlikely(ZERO_OR_NULL_PTR(fa))) + return 0; + if (element_nr >= fa->total_nr_elements) return -ENOSPC; if (elements_fit_in_base(fa)) @@ -215,6 +226,9 @@ int flex_array_clear(struct flex_array *fa, unsigned int element_nr) struct flex_array_part *part; void *dst; + if (unlikely(ZERO_OR_NULL_PTR(fa))) + return 0; + if (element_nr >= fa->total_nr_elements) return -ENOSPC; if (elements_fit_in_base(fa)) @@ -252,6 +266,9 @@ int flex_array_prealloc(struct flex_array *fa, unsigned int start, int part_nr; struct flex_array_part *part; + if (unlikely(ZERO_OR_NULL_PTR(fa))) + return 0; + if (start >= fa->total_nr_elements || end >= fa->total_nr_elements) return -ENOSPC; if (elements_fit_in_base(fa)) @@ -284,6 +301,9 @@ void *flex_array_get(struct flex_array *fa, unsigned int element_nr) int part_nr = fa_element_to_part_nr(fa, element_nr); struct flex_array_part *part; + if (unlikely(ZERO_OR_NULL_PTR(fa))) + return NULL; + if (element_nr >= fa->total_nr_elements) return NULL; if (elements_fit_in_base(fa)) @@ -343,6 +363,9 @@ int flex_array_shrink(struct flex_array *fa) int part_nr; int ret = 0; + if (unlikely(ZERO_OR_NULL_PTR(fa))) + return 0; + if (elements_fit_in_base(fa)) return ret; for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) { -- 1.7.0.4
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