From 26982a89cad77c0efc1c0c79bee0e3d75e9281d4 Mon Sep 17 00:00:00 2001 From: David Howells Date: Mon, 21 Dec 2020 22:37:58 +0000 Subject: afs: Work around strnlen() oops with CONFIG_FORTIFIED_SOURCE=y AFS has a structured layout in its directory contents (AFS dirs are downloaded as files and parsed locally by the client for lookup/readdir). The slots in the directory are defined by union afs_xdr_dirent. This, however, only directly allows a name of a length that will fit into that union. To support a longer name, the next 1-8 contiguous entries are annexed to the first one and the name flows across these. afs_dir_iterate_block() uses strnlen(), limited to the space to the end of the page, to find out how long the name is. This worked fine until 6a39e62abbaf. With that commit, the compiler determines the size of the array and asserts that the string fits inside that array. This is a problem for AFS because we *expect* it to overflow one or more arrays. A similar problem also occurs in afs_dir_scan_block() when a directory file is being locally edited to avoid the need to redownload it. There strlen() was being used safely because each page has the last byte set to 0 when the file is downloaded and validated (in afs_dir_check_page()). Fix this by changing the afs_xdr_dirent union name field to an indeterminate-length array and dropping the overflow field. (Note that whilst looking at this, I realised that the calculation of the number of slots a dirent used is non-standard and not quite right, but I'll address that in a separate patch.) The issue can be triggered by something like: touch /afs/example.com/thisisaveryveryverylongname and it generates a report that looks like: detected buffer overflow in strnlen ------------[ cut here ]------------ kernel BUG at lib/string.c:1149! ... RIP: 0010:fortify_panic+0xf/0x11 ... Call Trace: afs_dir_iterate_block+0x12b/0x35b afs_dir_iterate+0x14e/0x1ce afs_do_lookup+0x131/0x417 afs_lookup+0x24f/0x344 lookup_open.isra.0+0x1bb/0x27d open_last_lookups+0x166/0x237 path_openat+0xe0/0x159 do_filp_open+0x48/0xa4 ? kmem_cache_alloc+0xf5/0x16e ? __clear_close_on_exec+0x13/0x22 ? _raw_spin_unlock+0xa/0xb do_sys_openat2+0x72/0xde do_sys_open+0x3b/0x58 do_syscall_64+0x2d/0x3a entry_SYSCALL_64_after_hwframe+0x44/0xa9 Fixes: 6a39e62abbaf ("lib: string.h: detect intra-object overflow in fortified string functions") Reported-by: Marc Dionne Signed-off-by: David Howells Tested-by: Marc Dionne cc: Daniel Axtens --- fs/afs/xdr_fs.h | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/fs/afs/xdr_fs.h b/fs/afs/xdr_fs.h index 94f1f398eefa..c926430fd08a 100644 --- a/fs/afs/xdr_fs.h +++ b/fs/afs/xdr_fs.h @@ -54,10 +54,15 @@ union afs_xdr_dirent { __be16 hash_next; __be32 vnode; __be32 unique; - u8 name[16]; - u8 overflow[4]; /* if any char of the name (inc - * NUL) reaches here, consume - * the next dirent too */ + u8 name[]; + /* When determining the number of dirent slots needed to + * represent a directory entry, name should be assumed to be 16 + * bytes, due to a now-standardised (mis)calculation, but it is + * in fact 20 bytes in size. + * + * For names longer than (16 or) 20 bytes, extra slots should + * be annexed to this one using the extended_name format. + */ } u; u8 extended_name[32]; } __packed; -- cgit v1.2.3 From 366911cd762db02c2dd32fad1be96b72a66f205d Mon Sep 17 00:00:00 2001 From: David Howells Date: Wed, 23 Dec 2020 10:39:57 +0000 Subject: afs: Fix directory entry size calculation The number of dirent records used by an AFS directory entry should be calculated using the assumption that there is a 16-byte name field in the first block, rather than a 20-byte name field (which is actually the case). This miscalculation is historic and effectively standard, so we have to use it. The calculation we need to use is: 1 + (((strlen(name) + 1) + 15) >> 5) where we are adding one to the strlen() result to account for the NUL termination. Fix this by the following means: (1) Create an inline function to do the calculation for a given name length. (2) Use the function to calculate the number of records used for a dirent in afs_dir_iterate_block(). Use this to move the over-end check out of the loop since it only needs to be done once. Further use this to only go through the loop for the 2nd+ records composing an entry. The only test there now is for if the record is allocated - and we already checked the first block at the top of the outer loop. (3) Add a max name length check in afs_dir_iterate_block(). (4) Make afs_edit_dir_add() and afs_edit_dir_remove() use the function from (1) to calculate the number of blocks rather than doing it incorrectly themselves. Fixes: 63a4681ff39c ("afs: Locally edit directory data for mkdir/create/unlink/...") Fixes: ^1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: David Howells Tested-by: Marc Dionne --- fs/afs/dir.c | 49 ++++++++++++++++++++++++---------------------- fs/afs/dir_edit.c | 6 ++---- fs/afs/xdr_fs.h | 14 ++++++++++++- include/trace/events/afs.h | 2 ++ 4 files changed, 43 insertions(+), 28 deletions(-) diff --git a/fs/afs/dir.c b/fs/afs/dir.c index 9068d5578a26..7bd659ad959e 100644 --- a/fs/afs/dir.c +++ b/fs/afs/dir.c @@ -350,7 +350,7 @@ static int afs_dir_iterate_block(struct afs_vnode *dvnode, unsigned blkoff) { union afs_xdr_dirent *dire; - unsigned offset, next, curr; + unsigned offset, next, curr, nr_slots; size_t nlen; int tmp; @@ -363,13 +363,12 @@ static int afs_dir_iterate_block(struct afs_vnode *dvnode, offset < AFS_DIR_SLOTS_PER_BLOCK; offset = next ) { - next = offset + 1; - /* skip entries marked unused in the bitmap */ if (!(block->hdr.bitmap[offset / 8] & (1 << (offset % 8)))) { _debug("ENT[%zu.%u]: unused", blkoff / sizeof(union afs_xdr_dir_block), offset); + next = offset + 1; if (offset >= curr) ctx->pos = blkoff + next * sizeof(union afs_xdr_dirent); @@ -381,35 +380,39 @@ static int afs_dir_iterate_block(struct afs_vnode *dvnode, nlen = strnlen(dire->u.name, sizeof(*block) - offset * sizeof(union afs_xdr_dirent)); + if (nlen > AFSNAMEMAX - 1) { + _debug("ENT[%zu]: name too long (len %u/%zu)", + blkoff / sizeof(union afs_xdr_dir_block), + offset, nlen); + return afs_bad(dvnode, afs_file_error_dir_name_too_long); + } _debug("ENT[%zu.%u]: %s %zu \"%s\"", blkoff / sizeof(union afs_xdr_dir_block), offset, (offset < curr ? "skip" : "fill"), nlen, dire->u.name); - /* work out where the next possible entry is */ - for (tmp = nlen; tmp > 15; tmp -= sizeof(union afs_xdr_dirent)) { - if (next >= AFS_DIR_SLOTS_PER_BLOCK) { - _debug("ENT[%zu.%u]:" - " %u travelled beyond end dir block" - " (len %u/%zu)", - blkoff / sizeof(union afs_xdr_dir_block), - offset, next, tmp, nlen); - return afs_bad(dvnode, afs_file_error_dir_over_end); - } - if (!(block->hdr.bitmap[next / 8] & - (1 << (next % 8)))) { - _debug("ENT[%zu.%u]:" - " %u unmarked extension (len %u/%zu)", + nr_slots = afs_dir_calc_slots(nlen); + next = offset + nr_slots; + if (next > AFS_DIR_SLOTS_PER_BLOCK) { + _debug("ENT[%zu.%u]:" + " %u extends beyond end dir block" + " (len %zu)", + blkoff / sizeof(union afs_xdr_dir_block), + offset, next, nlen); + return afs_bad(dvnode, afs_file_error_dir_over_end); + } + + /* Check that the name-extension dirents are all allocated */ + for (tmp = 1; tmp < nr_slots; tmp++) { + unsigned int ix = offset + tmp; + if (!(block->hdr.bitmap[ix / 8] & (1 << (ix % 8)))) { + _debug("ENT[%zu.u]:" + " %u unmarked extension (%u/%u)", blkoff / sizeof(union afs_xdr_dir_block), - offset, next, tmp, nlen); + offset, tmp, nr_slots); return afs_bad(dvnode, afs_file_error_dir_unmarked_ext); } - - _debug("ENT[%zu.%u]: ext %u/%zu", - blkoff / sizeof(union afs_xdr_dir_block), - next, tmp, nlen); - next++; } /* skip if starts before the current position */ diff --git a/fs/afs/dir_edit.c b/fs/afs/dir_edit.c index 2ffe09abae7f..f4600c1353ad 100644 --- a/fs/afs/dir_edit.c +++ b/fs/afs/dir_edit.c @@ -215,8 +215,7 @@ void afs_edit_dir_add(struct afs_vnode *vnode, } /* Work out how many slots we're going to need. */ - need_slots = round_up(12 + name->len + 1 + 4, AFS_DIR_DIRENT_SIZE); - need_slots /= AFS_DIR_DIRENT_SIZE; + need_slots = afs_dir_calc_slots(name->len); meta_page = kmap(page0); meta = &meta_page->blocks[0]; @@ -393,8 +392,7 @@ void afs_edit_dir_remove(struct afs_vnode *vnode, } /* Work out how many slots we're going to discard. */ - need_slots = round_up(12 + name->len + 1 + 4, AFS_DIR_DIRENT_SIZE); - need_slots /= AFS_DIR_DIRENT_SIZE; + need_slots = afs_dir_calc_slots(name->len); meta_page = kmap(page0); meta = &meta_page->blocks[0]; diff --git a/fs/afs/xdr_fs.h b/fs/afs/xdr_fs.h index c926430fd08a..8ca868164507 100644 --- a/fs/afs/xdr_fs.h +++ b/fs/afs/xdr_fs.h @@ -58,7 +58,8 @@ union afs_xdr_dirent { /* When determining the number of dirent slots needed to * represent a directory entry, name should be assumed to be 16 * bytes, due to a now-standardised (mis)calculation, but it is - * in fact 20 bytes in size. + * in fact 20 bytes in size. afs_dir_calc_slots() should be + * used for this. * * For names longer than (16 or) 20 bytes, extra slots should * be annexed to this one using the extended_name format. @@ -101,4 +102,15 @@ struct afs_xdr_dir_page { union afs_xdr_dir_block blocks[AFS_DIR_BLOCKS_PER_PAGE]; }; +/* + * Calculate the number of dirent slots required for any given name length. + * The calculation is made assuming the part of the name in the first slot is + * 16 bytes, rather than 20, but this miscalculation is now standardised. + */ +static inline unsigned int afs_dir_calc_slots(size_t name_len) +{ + name_len++; /* NUL-terminated */ + return 1 + ((name_len + 15) / AFS_DIR_DIRENT_SIZE); +} + #endif /* XDR_FS_H */ diff --git a/include/trace/events/afs.h b/include/trace/events/afs.h index 4eef374d4413..4a5cc8c64be3 100644 --- a/include/trace/events/afs.h +++ b/include/trace/events/afs.h @@ -231,6 +231,7 @@ enum afs_file_error { afs_file_error_dir_bad_magic, afs_file_error_dir_big, afs_file_error_dir_missing_page, + afs_file_error_dir_name_too_long, afs_file_error_dir_over_end, afs_file_error_dir_small, afs_file_error_dir_unmarked_ext, @@ -488,6 +489,7 @@ enum afs_cb_break_reason { EM(afs_file_error_dir_bad_magic, "DIR_BAD_MAGIC") \ EM(afs_file_error_dir_big, "DIR_BIG") \ EM(afs_file_error_dir_missing_page, "DIR_MISSING_PAGE") \ + EM(afs_file_error_dir_name_too_long, "DIR_NAME_TOO_LONG") \ EM(afs_file_error_dir_over_end, "DIR_ENT_OVER_END") \ EM(afs_file_error_dir_small, "DIR_SMALL") \ EM(afs_file_error_dir_unmarked_ext, "DIR_UNMARKED_EXT") \ -- cgit v1.2.3