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authorThadeu Lima de Souza Cascardo <cascardo@canonical.com>2018-06-07 17:11:01 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-06-26 08:08:09 +0800
commitf3e7234932eb6a459963b13899241357306fae32 (patch)
parent9681c3bdb098f6c87a0422b6b63912c1b90ad197 (diff)
fs/binfmt_misc.c: do not allow offset overflow
commit 5cc41e099504b77014358b58567c5ea6293dd220 upstream. WHen registering a new binfmt_misc handler, it is possible to overflow the offset to get a negative value, which might crash the system, or possibly leak kernel data. Here is a crash log when 2500000000 was used as an offset: BUG: unable to handle kernel paging request at ffff989cfd6edca0 IP: load_misc_binary+0x22b/0x470 [binfmt_misc] PGD 1ef3e067 P4D 1ef3e067 PUD 0 Oops: 0000 [#1] SMP NOPTI Modules linked in: binfmt_misc kvm_intel ppdev kvm irqbypass joydev input_leds serio_raw mac_hid parport_pc qemu_fw_cfg parpy CPU: 0 PID: 2499 Comm: bash Not tainted 4.15.0-22-generic #24-Ubuntu Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.1-1 04/01/2014 RIP: 0010:load_misc_binary+0x22b/0x470 [binfmt_misc] Call Trace: search_binary_handler+0x97/0x1d0 do_execveat_common.isra.34+0x667/0x810 SyS_execve+0x31/0x40 do_syscall_64+0x73/0x130 entry_SYSCALL_64_after_hwframe+0x3d/0xa2 Use kstrtoint instead of simple_strtoul. It will work as the code already set the delimiter byte to '\0' and we only do it when the field is not empty. Tested with offsets -1, 2500000000, UINT_MAX and INT_MAX. Also tested with examples documented at Documentation/admin-guide/binfmt-misc.rst and other registrations from packages on Ubuntu. Link: http://lkml.kernel.org/r/20180529135648.14254-1-cascardo@canonical.com Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 9 insertions, 3 deletions
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 9b4688ab1d8e..f842261ce973 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -384,8 +384,13 @@ static Node *create_entry(const char __user *buffer, size_t count)
s = strchr(p, del);
if (!s)
goto einval;
- *s++ = '\0';
- e->offset = simple_strtoul(p, &p, 10);
+ *s = '\0';
+ if (p != s) {
+ int r = kstrtoint(p, 10, &e->offset);
+ if (r != 0 || e->offset < 0)
+ goto einval;
+ }
+ p = s;
if (*p++)
goto einval;
pr_debug("register: offset: %#x\n", e->offset);
@@ -425,7 +430,8 @@ static Node *create_entry(const char __user *buffer, size_t count)
if (e->mask &&
string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
goto einval;
- if (e->size + e->offset > BINPRM_BUF_SIZE)
+ if (e->size > BINPRM_BUF_SIZE ||
+ BINPRM_BUF_SIZE - e->size < e->offset)
goto einval;
pr_debug("register: magic/mask length: %i\n", e->size);
if (USE_DEBUG) {