zram: fix zstd dict use-after-free on per-CPU error path#1015
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June 29, 2026 17:40
zstd_setup_params() creates global cdict and ddict stored in params->drv_data, shared across all per-CPU contexts. When a per-CPU zstd_create() failed, its error path called zstd_release_params() which freed those shared objects while other per-CPU contexts might already hold references to them. Remove the premature zstd_release_params() from the per-CPU error path, the global cdict/ddict are properly released later by zstd_release_params(), called from zcomp_init()'s cleanup or from zcomp_destroy(). Fixes: 6a559ec ("zram: add dictionary support to zstd backend") Signed-off-by: Haoqin Huang <haoqinhuang@tencent.com> Reviewed-by: Rongwei Wang <zigiwang@tencent.com>
Writing dict or level parameters for algorithms that don't support them was silently accepted but had no effect. Out-of-range levels were silently clamped by the underlying library. Dict read failures always lost the real error from kernel_read_file_from_path(). Add caps, level_min and level_max to zcomp_ops and validate user-supplied parameters in algorithm_params_store() before storing, giving immediate error feedback. Also fix comp_params_store() to read the new dict into a temporary buffer before resetting old parameters, making the update atomic. Signed-off-by: Haoqin Huang <haoqinhuang@tencent.com> Reviewed-by: Rongwei Wang <zigiwang@tencent.com>
Parameters validated against one algorithm may be invalid for another (e.g. lz4 accepts level=65535 but zstd does not). Although algorithm changes are blocked after disksize is set, they are allowed before device initialization. Reset per-priority params on algorithm change so that stale parameters do not silently carry over. Signed-off-by: Haoqin Huang <haoqinhuang@tencent.com> Reviewed-by: Rongwei Wang <zigiwang@tencent.com>
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Pull request for series with
subject: zram: fix zstd dict use-after-free on per-CPU error path
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1117398