On 09/20/2016 04:01 PM, Kees Cook wrote:
On Tue, Sep 20, 2016 at 8:56 AM, Laura Abbott wrote:
While running a compile on arm64, I hit a memory exposure
usercopy: kernel memory exposure attempt detected from fcf3b1a8
(buffer_head) (1 bytes)
[ cut here ]
kernel BUG at mm/usercopy.c:75!
Internal error: Oops - BUG: 0 [#1] SMP
Modules linked in: ip6t_rpfilter ip6t_REJECT
nf_reject_ipv6 xt_conntrack ip_set nfnetlink ebtable_broute bridge stp
llc ebtable_nat ip6table_security ip6table_raw ip6table_nat
nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle
iptable_security iptable_raw iptable_nat nf_conntrack_ipv4
nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle
ebtable_filter ebtables ip6table_filter ip6_tables vfat fat xgene_edac
xgene_enet edac_core i2c_xgene_slimpro i2c_core at803x realtek xgene_dma
mdio_xgene gpio_dwapb gpio_xgene_sb xgene_rng mailbox_xgene_slimpro nfsd
auth_rpcgss nfs_acl lockd grace sunrpc xfs libcrc32c sdhci_of_arasan
sdhci_pltfm sdhci mmc_core xhci_plat_hcd gpio_keys
CPU: 0 PID: 19744 Comm: updatedb Tainted: GW 4.8.0-rc3-threadinfo+ #1
Hardware name: AppliedMicro X-Gene Mustang Board/X-Gene Mustang Board, BIOS
3.06.12 Aug 12 2016
task: fe03df944c00 task.stack: fe00d128c000
PC is at __check_object_size+0x70/0x3f0
LR is at __check_object_size+0x70/0x3f0
...
[] __check_object_size+0x70/0x3f0
[] filldir64+0x158/0x1a0
[] __fat_readdir+0x4a0/0x558 [fat]
[] fat_readdir+0x34/0x40 [fat]
[] iterate_dir+0x190/0x1e0
[] SyS_getdents64+0x88/0x120
[] el0_svc_naked+0x24/0x28
fcf3b1a8 is a module address. Modules may have compiled in
strings which could get copied to userspace. In this instance, it
looks like "." which matches with a size of 1 byte. Extend the
is_vmalloc_addr check to be is_vmalloc_or_module_addr to cover
all possible cases.
Signed-off-by: Laura Abbott
---
Longer term, it would be good to expand the check for to regions like
regular kernel memory.
---
mm/usercopy.c | 5 -
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/usercopy.c b/mm/usercopy.c
index 8ebae91..d8b5bd3 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -145,8 +145,11 @@ static inline const char *check_heap_object(const void
*ptr, unsigned long n,
* Some architectures (arm64) return true for virt_addr_valid() on
* vmalloced addresses. Work around this by checking for vmalloc
* first.
+*
+* We also need to check for module addresses explicitly since we
+* may copy static data from modules to userspace
*/
- if (is_vmalloc_addr(ptr))
+ if (is_vmalloc_or_module_addr(ptr))
return NULL;
I still don't understand why this happens on arm64 and not x86.
(Really what I don't understand is what virt_addr_valid() is actually
checking -- they seem to be checking very different things between x86
and arm64.)
virt_addr_valid is supposed to return true if and only if virt_to_page
returns a valid pointer. arm64 is currently returning true in some
cases it shouldn't. I finally got to work on a patch to fix it up so
hopefully once that gets submitted we can drop these extra checks.
Regardless, I'll get this pushed to Linus and try to make the -rc8 cut.
Thanks!
-Kees
if (!virt_addr_valid(ptr))
--
2.7.4
