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authorDaniel Borkmann <daniel@iogearbox.net>2018-01-10 23:25:05 +0100
committerAlexei Starovoitov <ast@kernel.org>2018-01-10 14:46:39 -0800
commitbbeb6e4323dad9b5e0ee9f60c223dd532e2403b1 (patch)
tree41ae826df7e3369e27a24c0936322b832f895dff /kernel
parent7891a87efc7116590eaba57acc3c422487802c6f (diff)
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bpf, array: fix overflow in max_entries and undefined behavior in index_mask
syzkaller tried to alloc a map with 0xfffffffd entries out of a userns, and thus unprivileged. With the recently added logic in b2157399cc98 ("bpf: prevent out-of-bounds speculation") we round this up to the next power of two value for max_entries for unprivileged such that we can apply proper masking into potentially zeroed out map slots. However, this will generate an index_mask of 0xffffffff, and therefore a + 1 will let this overflow into new max_entries of 0. This will pass allocation, etc, and later on map access we still enforce on the original attr->max_entries value which was 0xfffffffd, therefore triggering GPF all over the place. Thus bail out on overflow in such case. Moreover, on 32 bit archs roundup_pow_of_two() can also not be used, since fls_long(max_entries - 1) can result in 32 and 1UL << 32 in 32 bit space is undefined. Therefore, do this by hand in a 64 bit variable. This fixes all the issues triggered by syzkaller's reproducers. Fixes: b2157399cc98 ("bpf: prevent out-of-bounds speculation") Reported-by: syzbot+b0efb8e572d01bce1ae0@syzkaller.appspotmail.com Reported-by: syzbot+6c15e9744f75f2364773@syzkaller.appspotmail.com Reported-by: syzbot+d2f5524fb46fd3b312ee@syzkaller.appspotmail.com Reported-by: syzbot+61d23c95395cc90dbc2b@syzkaller.appspotmail.com Reported-by: syzbot+0d363c942452cca68c01@syzkaller.appspotmail.com Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/arraymap.c18
1 files changed, 15 insertions, 3 deletions
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index aaa319848e7d..ab94d304a634 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -56,7 +56,7 @@ static struct bpf_map *array_map_alloc(union bpf_attr *attr)
u32 elem_size, index_mask, max_entries;
bool unpriv = !capable(CAP_SYS_ADMIN);
struct bpf_array *array;
- u64 array_size;
+ u64 array_size, mask64;
/* check sanity of attributes */
if (attr->max_entries == 0 || attr->key_size != 4 ||
@@ -74,13 +74,25 @@ static struct bpf_map *array_map_alloc(union bpf_attr *attr)
elem_size = round_up(attr->value_size, 8);
max_entries = attr->max_entries;
- index_mask = roundup_pow_of_two(max_entries) - 1;
- if (unpriv)
+ /* On 32 bit archs roundup_pow_of_two() with max_entries that has
+ * upper most bit set in u32 space is undefined behavior due to
+ * resulting 1U << 32, so do it manually here in u64 space.
+ */
+ mask64 = fls_long(max_entries - 1);
+ mask64 = 1ULL << mask64;
+ mask64 -= 1;
+
+ index_mask = mask64;
+ if (unpriv) {
/* round up array size to nearest power of 2,
* since cpu will speculate within index_mask limits
*/
max_entries = index_mask + 1;
+ /* Check for overflows. */
+ if (max_entries < attr->max_entries)
+ return ERR_PTR(-E2BIG);
+ }
array_size = sizeof(*array);
if (percpu)