This is a note to let you know that I've just added the patch titled
bpf, array: fix overflow in max_entries and undefined behavior in index_mask
to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: bpf-array-fix-overflow-in-max_entries-and-undefined-behavior-in-index_mask.patch and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From bbeb6e4323dad9b5e0ee9f60c223dd532e2403b1 Mon Sep 17 00:00:00 2001
From: Daniel Borkmann daniel@iogearbox.net Date: Wed, 10 Jan 2018 23:25:05 +0100 Subject: bpf, array: fix overflow in max_entries and undefined behavior in index_mask
From: Daniel Borkmann daniel@iogearbox.net
commit bbeb6e4323dad9b5e0ee9f60c223dd532e2403b1 upstream.
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 Cc: Jiri Slaby jslaby@suse.cz Cc: Eric Dumazet eric.dumazet@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/bpf/arraymap.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)
--- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c @@ -53,7 +53,7 @@ static struct bpf_map *array_map_alloc(u 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 || @@ -70,13 +70,25 @@ static struct bpf_map *array_map_alloc(u 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)
Patches currently in stable-queue which might be from daniel@iogearbox.net are
queue-4.14/bpf-array-fix-overflow-in-max_entries-and-undefined-behavior-in-index_mask.patch queue-4.14/bpf-prevent-out-of-bounds-speculation.patch queue-4.14/bpf-arsh-is-not-supported-in-32-bit-alu-thus-reject-it.patch