On Mon, Feb 25, 2019 at 01:57:51PM -0500, Jeff Mahoney wrote:
> On 2/13/19 3:48 PM, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >
> > XFS had a use-after-free bug when xfs_xattr_put_listent runs out of
> > listxattr buffer space while trying to store the name
> > "system.posix_acl_access" and then corrupts memory by not checking the
> > seen_enough state and then trying to shove "trusted.SGI_ACL_FILE" into
> > the buffer as well.
> >
> > In order to tickle the bug in a user visible way we must have already
> > put a name in the buffer, so we take advantage of the fact that
> > "security.evm" sorts before "system.posix_acl_access" to make sure this
> > happens.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
>
> [...]
>
> > +
> > +int main(int argc, char *argv[])
> > +{
> > + struct myacl acl = {
> > + .d = 2,
> > + .e = {
> > + {1, 0, 0},
> > + {4, 0, 0},
> > + {0x10, 0, 0},
> > + {0x20, 0, 0},
> > + },
> > + };
> > + char buf[64];
> > + ssize_t sz;
> > + int fd;
> > + int ret;
> > +
> > + if (argc > 1) {
> > + ret = chdir(argv[1]);
> > + if (ret)
> > + die(argv[1]);
> > + }
> > +
> > + fd = creat("file0", 0644);
> > + if (fd < 0)
> > + die("create");
> > +
> > + ret = fsetxattr(fd, "system.posix_acl_access", &acl, sizeof(acl), 0);
> > + if (ret)
> > + die("set posix acl");
> > +
> > + ret = fsetxattr(fd, "security.evm", buf, 1, 1);
> > + if (ret)
> > + die("set evm");
>
> How is this working on your test system?
CONFIG_EVM=n, that's how. :(
> The EVM xattr is a formatted structure and this is passing it an
> uninitialized buffer. It *should* return EPERM and on our test
> systems it is.
Er... what is the structure of the evm attr, anyway? Does passing in a
single byte 0x03 actually work?
Oh, it's in security/integrity/integrity.h, that's why I couldn't find
it....
enum evm_ima_xattr_type {
IMA_XATTR_DIGEST = 0x01,
EVM_XATTR_HMAC,
EVM_IMA_XATTR_DIGSIG,
IMA_XATTR_DIGEST_NG,
EVM_XATTR_PORTABLE_DIGSIG,
IMA_XATTR_LAST
};
struct evm_ima_xattr_data {
u8 type;
u8 digest[SHA1_DIGEST_SIZE];
} __packed;
So I guess we're passing in a xattr_data of type EVM_IMA_XATTR_DIGSIG?
With no actual digest information, which seems suspect to me.
Now I wonder if the VM they used to generate the syzkaller report has
EVM enabled....
(And this is why I hate syzkaller reports, all of the mechanisation I
can't (under)stand and none of the context to help me write a decent
regression test case that actually just friggin works.)
> Using security.capability will sort before system.posix_acl_access and
> accepts unformatted contents.
I'll try that and report back, thank you. Sorry for the mess.
--D
> -Jeff
>
> > + sz = flistxattr(fd, buf, 30);
> > + if (sz < 0)
> > + die("list attr");
> > +
> > + printf("%s\n", buf);
> > +
> > + return 0;
> > +
> > +#if 0
> > + /* original syzkaller reproducer */
> > +
> > + syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);
> > +
> > + memcpy((void*)0x20000180, "./file0", 8);
> > + syscall(__NR_creat, 0x20000180, 0);
> > + memcpy((void*)0x20000000, "./file0", 8);
> > + memcpy((void*)0x20000040, "system.posix_acl_access", 24);
> > + *(uint32_t*)0x20000680 = 2;
> > + *(uint16_t*)0x20000684 = 1;
> > + *(uint16_t*)0x20000686 = 0;
> > + *(uint32_t*)0x20000688 = 0;
> > + *(uint16_t*)0x2000068c = 4;
> > + *(uint16_t*)0x2000068e = 0;
> > + *(uint32_t*)0x20000690 = 0;
> > + *(uint16_t*)0x20000694 = 0x10;
> > + *(uint16_t*)0x20000696 = 0;
> > + *(uint32_t*)0x20000698 = 0;
> > + *(uint16_t*)0x2000069c = 0x20;
> > + *(uint16_t*)0x2000069e = 0;
> > + *(uint32_t*)0x200006a0 = 0;
> > + syscall(__NR_setxattr, 0x20000000, 0x20000040, 0x20000680, 0x24, 0);
> > + memcpy((void*)0x20000080, "./file0", 8);
> > + memcpy((void*)0x200000c0, "security.evm", 13);
> > + memcpy((void*)0x20000100, "\x03\x00\x00\x00\x57", 5);
> > + syscall(__NR_lsetxattr, 0x20000080, 0x200000c0, 0x20000100, 1, 1);
> > + memcpy((void*)0x20000300, "./file0", 8);
> > + syscall(__NR_listxattr, 0x20000300, 0x200002c0, 0x1e);
> > + return 0;
> > +#endif
> > +}
>
>
>
> --
> Jeff Mahoney
> SUSE Labs
