From: Michael Bommarito Date: Tue, 14 Jul 2026 11:47:29 +0000 (-0400) Subject: erofs: cap LZMA stream pool size X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c9b47e6b23114e939b17f818471c7a46e59006e7;p=thirdparty%2Flinux.git erofs: cap LZMA stream pool size fs/erofs/decompressor_lzma.c sizes the module-global MicroLZMA stream pool from num_possible_cpus() when the lzma_streams module parameter is unset, then z_erofs_load_lzma_config() preallocates one image-supplied dictionary per stream, accepting dictionaries up to 8 MiB. On high-CPU systems, a small EROFS image can pin hundreds of MiB of vmalloc-backed decoder state until the erofs module is unloaded. Impact: An EROFS image mounted by the system can pin up to 8 MiB of vmalloc memory per LZMA stream, either as intended or unexpectedly. Bound the default stream count by a new CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS option, default 16, so the worst-case default preallocation is 128 MiB if the number of CPUs is no less than 16 while preserving the existing per-image dictionary limit. An explicit lzma_streams module parameter is still honoured as-is, so administrators who deliberately size the pool are not affected. Fixes: 622ceaddb764 ("erofs: lzma compression support") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Michael Bommarito Reviewed-by: Gao Xiang Signed-off-by: Gao Xiang --- diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig index 1feb28cfe557..8ca1767dafb6 100644 --- a/fs/erofs/Kconfig +++ b/fs/erofs/Kconfig @@ -131,6 +131,20 @@ config EROFS_FS_ZIP_LZMA Say N if you want to disable LZMA compression support. +config EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS + int "EROFS LZMA default maximum decompression streams" + depends on EROFS_FS_ZIP_LZMA + range 1 NR_CPUS + default 16 + help + By default EROFS allocates one LZMA decompression stream per CPU. + Each stream can hold a dictionary of up to 8 MiB taken from the + mounted image, so on systems with many CPUs this can reserve a lot + of memory. This caps the default; the lzma_streams module parameter + still overrides it. + + If unsure, keep the default of 16. + config EROFS_FS_ZIP_DEFLATE bool "EROFS DEFLATE compressed data support" depends on EROFS_FS_ZIP diff --git a/fs/erofs/decompressor_lzma.c b/fs/erofs/decompressor_lzma.c index f6692d0f2f04..6b0cdb446c6a 100644 --- a/fs/erofs/decompressor_lzma.c +++ b/fs/erofs/decompressor_lzma.c @@ -51,7 +51,8 @@ static int __init z_erofs_lzma_init(void) /* by default, use # of possible CPUs instead */ if (!z_erofs_lzma_nstrms) - z_erofs_lzma_nstrms = num_possible_cpus(); + z_erofs_lzma_nstrms = min_t(unsigned int, num_possible_cpus(), + CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS); for (i = 0; i < z_erofs_lzma_nstrms; ++i) { struct z_erofs_lzma *strm = kzalloc_obj(*strm);