3.16.62-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Jeremy Cline <jcline@xxxxxxxxxx> commit 1a5d5e5d51e75a5bca67dadbcea8c841934b7b85 upstream. 'ac->ac_g_ex.fe_len' is a user-controlled value which is used in the derivation of 'ac->ac_2order'. 'ac->ac_2order', in turn, is used to index arrays which makes it a potential spectre gadget. Fix this by sanitizing the value assigned to 'ac->ac2_order'. This covers the following accesses found with the help of smatch: * fs/ext4/mballoc.c:1896 ext4_mb_simple_scan_group() warn: potential spectre issue 'grp->bb_counters' [w] (local cap) * fs/ext4/mballoc.c:445 mb_find_buddy() warn: potential spectre issue 'EXT4_SB(e4b->bd_sb)->s_mb_offsets' [r] (local cap) * fs/ext4/mballoc.c:446 mb_find_buddy() warn: potential spectre issue 'EXT4_SB(e4b->bd_sb)->s_mb_maxs' [r] (local cap) Suggested-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Signed-off-by: Jeremy Cline <jcline@xxxxxxxxxx> Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- fs/ext4/mballoc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -26,6 +26,7 @@ #include <linux/log2.h> #include <linux/module.h> #include <linux/slab.h> +#include <linux/nospec.h> #include <trace/events/ext4.h> #ifdef CONFIG_EXT4_DEBUG @@ -2124,7 +2125,8 @@ ext4_mb_regular_allocator(struct ext4_al * This should tell if fe_len is exactly power of 2 */ if ((ac->ac_g_ex.fe_len & (~(1 << (i - 1)))) == 0) - ac->ac_2order = i - 1; + ac->ac_2order = array_index_nospec(i - 1, + sb->s_blocksize_bits + 2); } /* if stream allocation is enabled, use global goal */
