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[182.171.80.51]) by smtp.gmail.com with ESMTPSA id b17sm11969851pfr.17.2019.11.26.01.04.22 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Nov 2019 01:04:23 -0800 (PST) From: Wang Shilong To: linux-ext4@vger.kernel.org Cc: adilger@dilger.ca, lixi@ddn.com, wshilong@ddn.com Subject: [PATCH 2/2] e2fsck: fix use after free in calculate_tree() Date: Tue, 26 Nov 2019 18:03:59 +0900 Message-Id: <1574759039-7429-2-git-send-email-wangshilong1991@gmail.com> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1574759039-7429-1-git-send-email-wangshilong1991@gmail.com> References: <1574759039-7429-1-git-send-email-wangshilong1991@gmail.com> Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org From: Wang Shilong Hit following Seg errors randomly when running f_large_dir test: +Signal (11) SIGSEGV si_code=SEGV_MAPERR fault addr=0x7f02cfffbc1a +../e2fsck/e2fsck[0x43766e] +/lib64/libpthread.so.0(+0xf7e0)[0x7f02d8c9a7e0] +../e2fsck/e2fsck(e2fsck_rehash_dir+0x10f3)[0x436173] +../e2fsck/e2fsck(e2fsck_rehash_directories+0xf4)[0x4362d4] +../e2fsck/e2fsck(e2fsck_pass3+0x722)[0x4292c2] +../e2fsck/e2fsck(e2fsck_run+0x47)[0x414ef7] +../e2fsck/e2fsck(main+0x1c1d)[0x41319d] +/lib64/libc.so.6(__libc_start_main+0x100)[0x7f02d8915d20] +../e2fsck/e2fsck[0x40fc59] +Exit status is 8 gdb output is: 0x436173 is in e2fsck_rehash_dir (rehash.c:752). warning: Source file is more recent than executable. 747 dx_ent->hash = 748 ext2fs_cpu_to_le32(outdir->hashes[i]); 749 dx_ent++; 750 c3--; 751 } 752 int_limit->count = ext2fs_cpu_to_le16(limit->limit - c2); 753 int_limit->limit = ext2fs_cpu_to_le16(limit->limit); 754 755 limit->count = ext2fs_cpu_to_le16(limit->limit - c3); 756 limit->limit = ext2fs_cpu_to_le16(limit->limit); The problem is alloc_blocks() will call get_next_block() which might reallocate @outdir->buf, and memory address could be changed after this. @int_limit and @root should be recalculated based on new start address. Otherwise, it will try to access freed memory and cause SEGV_MAPERR errors. Signed-off-by: Wang Shilong --- e2fsck/rehash.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/e2fsck/rehash.c b/e2fsck/rehash.c index 5250652e..0eb99328 100644 --- a/e2fsck/rehash.c +++ b/e2fsck/rehash.c @@ -636,6 +636,9 @@ static int alloc_blocks(ext2_filsys fs, if (retval) return retval; + /* outdir->buf might be reallocated */ + *prev_ent = (struct ext2_dx_entry *) (outdir->buf + *prev_offset); + *next_ent = set_int_node(fs, block_start); *limit = (struct ext2_dx_countlimit *)(*next_ent); if (next_offset) @@ -725,12 +728,18 @@ static errcode_t calculate_tree(ext2_filsys fs, return retval; } if (c3 == 0) { + int delta1 = int_offset;; + int delta2 = (char *)root - outdir->buf; + retval = alloc_blocks(fs, &limit, &int_ent, &dx_ent, &int_offset, NULL, outdir, i, &c2, &c3); if (retval) return retval; + /* outdir->buf might be reallocated */ + int_limit = (struct ext2_dx_countlimit *)(outdir->buf + delta1); + root = (struct ext2_dx_entry *)(outdir->buf + delta2); } dx_ent->block = ext2fs_cpu_to_le32(i); -- 2.21.0