CVE ID:	CVE-2023-52759
Description:	In the Linux kernel, the following vulnerability has been resolved: gfs2: ignore negated quota changes When lots of quota changes are made, there may be cases in which an inode's quota information is increased and then decreased, such as when blocks are added to a file, then deleted from it. If the timing is right, function do_qc can add pending quota changes to a transaction, then later, another call to do_qc can negate those changes, resulting in a net gain of 0. The quota_change information is recorded in the qc buffer (and qd element of the inode as well). The buffer is added to the transaction by the first call to do_qc, but a subsequent call changes the value from non- zero back to zero. At that point it's too late to remove the buffer_head from the transaction. Later, when the quota sync code is called, the zero-change qd element is discovered and flagged as an assert warning. If the fs is mounted with errors=panic, the kernel will panic. This is usually seen when files are truncated and the quota changes are negated by punch_hole/truncate which uses gfs2_quota_hold and gfs2_quota_unhold rather than block allocations that use gfs2_quota_lock and gfs2_quota_unlock which automatically do quota sync. This patch solves the problem by adding a check to qd_check_sync such that net-zero quota changes already added to the transaction are no longer deemed necessary to be synced, and skipped. In this case references are taken for the qd and the slot from do_qc so those need to be put. The normal sequence of events for a normal non-zero quota change is as follows: gfs2_quota_change do_qc qd_hold slot_hold Later, when the changes are to be synced: gfs2_quota_sync qd_fish qd_check_sync gets qd ref via lockref_get_not_dead do_sync do_qc(QC_SYNC) qd_put lockref_put_or_lock qd_unlock qd_put lockref_put_or_lock In the net-zero change case, we add a check to qd_check_sync so it puts the qd and slot references acquired in gfs2_quota_change and skip the unneeded sync.
Test IDs:	None available
Cross References:	Common Vulnerability Exposure (CVE) ID: CVE-2023-52759 https://git.kernel.org/stable/c/119565e566f91ff3588ffcd5812f0c8061586c6b https://git.kernel.org/stable/c/119565e566f91ff3588ffcd5812f0c8061586c6b https://git.kernel.org/stable/c/1c28dace66015b675a343b89b0c87abbfda05ff4 https://git.kernel.org/stable/c/1c28dace66015b675a343b89b0c87abbfda05ff4 https://git.kernel.org/stable/c/212f112fe5e90e98eb8d48585682880dae139f4c https://git.kernel.org/stable/c/212f112fe5e90e98eb8d48585682880dae139f4c https://git.kernel.org/stable/c/2a054b87a1b799b391e578597a42ee6e57a987ae https://git.kernel.org/stable/c/2a054b87a1b799b391e578597a42ee6e57a987ae https://git.kernel.org/stable/c/2bb42a27a92ff3984c9fa5fbe128eced3ea693f2 https://git.kernel.org/stable/c/2bb42a27a92ff3984c9fa5fbe128eced3ea693f2 https://git.kernel.org/stable/c/4c6a08125f2249531ec01783a5f4317d7342add5 https://git.kernel.org/stable/c/4c6a08125f2249531ec01783a5f4317d7342add5 https://git.kernel.org/stable/c/53fc16c1ad84f5467ec24341670b63aa759335d3 https://git.kernel.org/stable/c/53fc16c1ad84f5467ec24341670b63aa759335d3 https://git.kernel.org/stable/c/5bfda356e903633d16ae1bac1ee38364e12628a3 https://git.kernel.org/stable/c/5bfda356e903633d16ae1bac1ee38364e12628a3 https://git.kernel.org/stable/c/b4deec69fe32b58dc5fb4ace52456ece85b75561 https://git.kernel.org/stable/c/b4deec69fe32b58dc5fb4ace52456ece85b75561