| Message ID | 155114853550.9683.11298191063436471344.stgit@magnolia (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] misc: don't oom the box opening tmpfiles | expand |
On 2/25/19 7:35 PM, Darrick J. Wong wrote: > From: Darrick J. Wong <darrick.wong@oracle.com> > > Jeff Moyer pointed out that 'security.evm' actually has an expected > value format, which breaks the test if EVM is enabled. It turns out > that the 'security.evm' setxattr call in the original syzkaller report > was a total red herring, as this bug can be reproduced without it. > > Fix the test case to do the minimum amount of work needed to reproduce > the corruption. > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> > --- > src/t_attr_corruption.c | 28 ++++++++++++++-------------- > 1 file changed, 14 insertions(+), 14 deletions(-) > > > diff --git a/src/t_attr_corruption.c b/src/t_attr_corruption.c > index f26611f9..9101024e 100644 > --- a/src/t_attr_corruption.c > +++ b/src/t_attr_corruption.c > @@ -3,17 +3,21 @@ > * Copyright (C) 2019 Oracle. All Rights Reserved. > * Author: Darrick J. Wong <darrick.wong@oracle.com> > * > - * Test program to tickle a use-after-free bug in xfs. > + * XFS had a memory corruption bug in its handling of the POSIX ACL attribute > + * names during a listxattr call. > * > - * 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. > + * On IRIX, file ACLs were stored under the name "trusted.SGI_ACL_FILE", > + * whereas on Linux the name is "system.posix_acl_access". In order to > + * maintain compatibility with old filesystems, XFS internally continues to > + * use the old SGI_ACL_FILE name on disk and remap the new name whenever it > + * sees it. > * > - * 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. > + * In order to make this magic happen, XFS' listxattr implementation will emit > + * first the Linux name and then the on-disk name. Unfortunately, it doesn't > + * correctly check the buffer length, so if the buffer is large enough to fit > + * the on-disk name but not large enough to fit the Linux name, we screw up > + * the buffer position accounting while trying to emit the Linux name and then > + * corrupt memory when we try to emit the on-disk name. Ok, thanks for the explanation! You can add my review: Reviewed-by: Allison Henderson <allison.henderson@oracle.com> > * > * If we trigger the bug, the program will print the garbled string > * "rusted.SGI_ACL_FILE". If the bug is fixed, the flistxattr call returns > @@ -76,11 +80,7 @@ int main(int argc, char *argv[]) > if (ret) > die("set posix acl"); > > - ret = fsetxattr(fd, "security.evm", buf, 1, 1); > - if (ret) > - die("set evm"); > - > - sz = flistxattr(fd, buf, 30); > + sz = flistxattr(fd, buf, 20); > if (sz < 0) > die("list attr"); > >
On 2/25/19 9:35 PM, Darrick J. Wong wrote: > From: Darrick J. Wong <darrick.wong@oracle.com> > > Jeff Moyer pointed out that 'security.evm' actually has an expected Mahoney :) > value format, which breaks the test if EVM is enabled. It turns out > that the 'security.evm' setxattr call in the original syzkaller report > was a total red herring, as this bug can be reproduced without it. > > Fix the test case to do the minimum amount of work needed to reproduce > the corruption. > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Otherwise, works for me in the case that failed for me previously. Thanks, -Jeff > --- > src/t_attr_corruption.c | 28 ++++++++++++++-------------- > 1 file changed, 14 insertions(+), 14 deletions(-) > > > diff --git a/src/t_attr_corruption.c b/src/t_attr_corruption.c > index f26611f9..9101024e 100644 > --- a/src/t_attr_corruption.c > +++ b/src/t_attr_corruption.c > @@ -3,17 +3,21 @@ > * Copyright (C) 2019 Oracle. All Rights Reserved. > * Author: Darrick J. Wong <darrick.wong@oracle.com> > * > - * Test program to tickle a use-after-free bug in xfs. > + * XFS had a memory corruption bug in its handling of the POSIX ACL attribute > + * names during a listxattr call. > * > - * 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. > + * On IRIX, file ACLs were stored under the name "trusted.SGI_ACL_FILE", > + * whereas on Linux the name is "system.posix_acl_access". In order to > + * maintain compatibility with old filesystems, XFS internally continues to > + * use the old SGI_ACL_FILE name on disk and remap the new name whenever it > + * sees it. > * > - * 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. > + * In order to make this magic happen, XFS' listxattr implementation will emit > + * first the Linux name and then the on-disk name. Unfortunately, it doesn't > + * correctly check the buffer length, so if the buffer is large enough to fit > + * the on-disk name but not large enough to fit the Linux name, we screw up > + * the buffer position accounting while trying to emit the Linux name and then > + * corrupt memory when we try to emit the on-disk name. > * > * If we trigger the bug, the program will print the garbled string > * "rusted.SGI_ACL_FILE". If the bug is fixed, the flistxattr call returns > @@ -76,11 +80,7 @@ int main(int argc, char *argv[]) > if (ret) > die("set posix acl"); > > - ret = fsetxattr(fd, "security.evm", buf, 1, 1); > - if (ret) > - die("set evm"); > - > - sz = flistxattr(fd, buf, 30); > + sz = flistxattr(fd, buf, 20); > if (sz < 0) > die("list attr"); > > >
On Thu, Feb 28, 2019 at 03:56:40PM -0500, Jeff Mahoney wrote: > On 2/25/19 9:35 PM, Darrick J. Wong wrote: > > From: Darrick J. Wong <darrick.wong@oracle.com> > > > > Jeff Moyer pointed out that 'security.evm' actually has an expected > > Mahoney :) Fixed on commit :) > > > value format, which breaks the test if EVM is enabled. It turns out > > that the 'security.evm' setxattr call in the original syzkaller report > > was a total red herring, as this bug can be reproduced without it. > > > > Fix the test case to do the minimum amount of work needed to reproduce > > the corruption. > > > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> > > Otherwise, works for me in the case that failed for me previously. Thanks for the fix and test! Eryu
diff --git a/src/t_attr_corruption.c b/src/t_attr_corruption.c index f26611f9..9101024e 100644 --- a/src/t_attr_corruption.c +++ b/src/t_attr_corruption.c @@ -3,17 +3,21 @@ * Copyright (C) 2019 Oracle. All Rights Reserved. * Author: Darrick J. Wong <darrick.wong@oracle.com> * - * Test program to tickle a use-after-free bug in xfs. + * XFS had a memory corruption bug in its handling of the POSIX ACL attribute + * names during a listxattr call. * - * 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. + * On IRIX, file ACLs were stored under the name "trusted.SGI_ACL_FILE", + * whereas on Linux the name is "system.posix_acl_access". In order to + * maintain compatibility with old filesystems, XFS internally continues to + * use the old SGI_ACL_FILE name on disk and remap the new name whenever it + * sees it. * - * 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. + * In order to make this magic happen, XFS' listxattr implementation will emit + * first the Linux name and then the on-disk name. Unfortunately, it doesn't + * correctly check the buffer length, so if the buffer is large enough to fit + * the on-disk name but not large enough to fit the Linux name, we screw up + * the buffer position accounting while trying to emit the Linux name and then + * corrupt memory when we try to emit the on-disk name. * * If we trigger the bug, the program will print the garbled string * "rusted.SGI_ACL_FILE". If the bug is fixed, the flistxattr call returns @@ -76,11 +80,7 @@ int main(int argc, char *argv[]) if (ret) die("set posix acl"); - ret = fsetxattr(fd, "security.evm", buf, 1, 1); - if (ret) - die("set evm"); - - sz = flistxattr(fd, buf, 30); + sz = flistxattr(fd, buf, 20); if (sz < 0) die("list attr");