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dabc8b2075
The dquot_mark_dquot_dirty() using dquot references from the inode
should be protected by dquot_srcu. quota_off code takes care to call
synchronize_srcu(&dquot_srcu) to not drop dquot references while they
are used by other users. But dquot_transfer() breaks this assumption.
We call dquot_transfer() to drop the last reference of dquot and add
it to free_dquots, but there may still be other users using the dquot
at this time, as shown in the function graph below:
cpu1 cpu2
_________________|_________________
wb_do_writeback CHOWN(1)
...
ext4_da_update_reserve_space
dquot_claim_block
...
dquot_mark_dquot_dirty // try to dirty old quota
test_bit(DQ_ACTIVE_B, &dquot->dq_flags) // still ACTIVE
if (test_bit(DQ_MOD_B, &dquot->dq_flags))
// test no dirty, wait dq_list_lock
...
dquot_transfer
__dquot_transfer
dqput_all(transfer_from) // rls old dquot
dqput // last dqput
dquot_release
clear_bit(DQ_ACTIVE_B, &dquot->dq_flags)
atomic_dec(&dquot->dq_count)
put_dquot_last(dquot)
list_add_tail(&dquot->dq_free, &free_dquots)
// add the dquot to free_dquots
if (!test_and_set_bit(DQ_MOD_B, &dquot->dq_flags))
add dqi_dirty_list // add released dquot to dirty_list
This can cause various issues, such as dquot being destroyed by
dqcache_shrink_scan() after being added to free_dquots, which can trigger
a UAF in dquot_mark_dquot_dirty(); or after dquot is added to free_dquots
and then to dirty_list, it is added to free_dquots again after
dquot_writeback_dquots() is executed, which causes the free_dquots list to
be corrupted and triggers a UAF when dqcache_shrink_scan() is called for
freeing dquot twice.
As Honza said, we need to fix dquot_transfer() to follow the guarantees
dquot_srcu should provide. But calling synchronize_srcu() directly from
dquot_transfer() is too expensive (and mostly unnecessary). So we add
dquot whose last reference should be dropped to the new global dquot
list releasing_dquots, and then queue work item which would call
synchronize_srcu() and after that perform the final cleanup of all the
dquots on releasing_dquots.
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.