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Levin" Subject: Re: [PATCH v5] 9pfs: Fix segfault in do_readdir_many caused by struct dirent overread Date: Thu, 17 Feb 2022 10:26:37 +0100 Message-ID: <1985849.zTV3lQ0sjB@silver> In-Reply-To: <20220216181821.3481527-1-vt@altlinux.org> References: <20220216181821.3481527-1-vt@altlinux.org> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Received-SPF: pass client-ip=5.189.157.229; envelope-from=qemu_oss@crudebyte.com; helo=kylie.crudebyte.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mittwoch, 16. Februar 2022 19:18:21 CET Vitaly Chikunov wrote: > `struct dirent' returned from readdir(3) could be shorter (or longer) > than `sizeof(struct dirent)', thus memcpy of sizeof length will overread > into unallocated page causing SIGSEGV. Example stack trace: > > #0 0x00005555559ebeed v9fs_co_readdir_many (/usr/bin/qemu-system-x86_64 + > 0x497eed) #1 0x00005555559ec2e9 v9fs_readdir (/usr/bin/qemu-system-x86_64 > + 0x4982e9) #2 0x0000555555eb7983 coroutine_trampoline > (/usr/bin/qemu-system-x86_64 + 0x963983) #3 0x00007ffff73e0be0 n/a (n/a + > 0x0) > > While fixing this, provide a helper for any future `struct dirent' cloning. > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841 > Cc: qemu-stable@nongnu.org > Co-authored-by: Christian Schoenebeck > Reviewed-by: Dmitry V. Levin > Signed-off-by: Vitaly Chikunov > --- > Tested on x68-64 Linux with btrfs-progs tests and qos-test -m slow. Consider donating your Tested-by tag then. > Changes since v4: > - Zero clear V9fsSynthOpenState on allocation. Uninitialised use of > d_reclen bug found by fuzzing. Use g_new0 instead of g_malloc0 as > Greg Kurz suggested. I can confirm that v4 triggered the previously discussed ASan error when running the 9p 'synth' tests; and with this v5 ASan no longer triggers an error. Tested-by: Christian Schoenebeck Maybe some of the new comments could be improved, for instance ... > > hw/9pfs/9p-synth.c | 18 +++++++++++++++--- > hw/9pfs/9p-synth.h | 5 +++++ > hw/9pfs/codir.c | 3 +-- > include/qemu/osdep.h | 13 +++++++++++++ > util/osdep.c | 21 +++++++++++++++++++++ > 5 files changed, 55 insertions(+), 5 deletions(-) > > diff --git a/hw/9pfs/9p-synth.c b/hw/9pfs/9p-synth.c > index b38088e066..396cda36f1 100644 > --- a/hw/9pfs/9p-synth.c > +++ b/hw/9pfs/9p-synth.c > @@ -182,7 +182,12 @@ static int synth_opendir(FsContext *ctx, > V9fsSynthOpenState *synth_open; > V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data; > > - synth_open = g_malloc(sizeof(*synth_open)); > + /* > + * V9fsSynthOpenState contains 'struct dirent' which have OS-specific > + * properties, thus it's zero cleared on allocation here and below > + * in synth_open. > + */ > + synth_open = g_new0(V9fsSynthOpenState, 1); > synth_open->node = node; > node->open_count++; > fs->private = synth_open; > @@ -220,7 +225,14 @@ static void synth_rewinddir(FsContext *ctx, > V9fsFidOpenState *fs) static void synth_direntry(V9fsSynthNode *node, > struct dirent *entry, off_t off) > { > - strcpy(entry->d_name, node->name); > + size_t sz = strlen(node->name) + 1; > + /* > + * 'entry' is always inside of V9fsSynthOpenState which have NAME_MAX > + * back padding. Ensure we do not orerflow it. > + */ ... here is a typo in the comment. But unless there are more issues, I could handle such minor comment issues on my end before pushing. Reviewed-by: Christian Schoenebeck Best regards, Christian Schoenebeck > + g_assert(sizeof(struct dirent) + NAME_MAX >= > + offsetof(struct dirent, d_name) + sz); > + memcpy(entry->d_name, node->name, sz); > entry->d_ino = node->attr->inode; > entry->d_off = off + 1; > } > @@ -266,7 +278,7 @@ static int synth_open(FsContext *ctx, V9fsPath *fs_path, > V9fsSynthOpenState *synth_open; > V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data; > > - synth_open = g_malloc(sizeof(*synth_open)); > + synth_open = g_new0(V9fsSynthOpenState, 1); > synth_open->node = node; > node->open_count++; > fs->private = synth_open; > diff --git a/hw/9pfs/9p-synth.h b/hw/9pfs/9p-synth.h > index 036d7e4a5b..eeb246f377 100644 > --- a/hw/9pfs/9p-synth.h > +++ b/hw/9pfs/9p-synth.h > @@ -41,6 +41,11 @@ typedef struct V9fsSynthOpenState { > off_t offset; > V9fsSynthNode *node; > struct dirent dent; > + /* > + * Ensure there is enough space for 'dent' above, some systems have a > + * d_name size of just 1, which would cause a buffer overrun. > + */ > + char dent_trailing_space[NAME_MAX]; > } V9fsSynthOpenState; > > int qemu_v9fs_synth_mkdir(V9fsSynthNode *parent, int mode, > diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c > index 032cce04c4..c0873bde16 100644 > --- a/hw/9pfs/codir.c > +++ b/hw/9pfs/codir.c > @@ -143,8 +143,7 @@ static int do_readdir_many(V9fsPDU *pdu, V9fsFidState > *fidp, } else { > e = e->next = g_malloc0(sizeof(V9fsDirEnt)); > } > - e->dent = g_malloc0(sizeof(struct dirent)); > - memcpy(e->dent, dent, sizeof(struct dirent)); > + e->dent = qemu_dirent_dup(dent); > > /* perform a full stat() for directory entry if requested by caller > */ if (dostat) { > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > index d1660d67fa..ce12f64853 100644 > --- a/include/qemu/osdep.h > +++ b/include/qemu/osdep.h > @@ -805,6 +805,19 @@ static inline int > platform_does_not_support_system(const char *command) } > #endif /* !HAVE_SYSTEM_FUNCTION */ > > +/** > + * Duplicate directory entry @dent. > + * > + * It is highly recommended to use this function instead of open coding > + * duplication of @c dirent objects, because the actual @c struct @c dirent > + * size may be bigger or shorter than @c sizeof(struct dirent) and correct > + * handling is platform specific (see gitlab issue #841). > + * > + * @dent - original directory entry to be duplicated > + * @returns duplicated directory entry which should be freed with g_free() > + */ > +struct dirent *qemu_dirent_dup(struct dirent *dent); > + > #ifdef __cplusplus > } > #endif > diff --git a/util/osdep.c b/util/osdep.c > index 42a0a4986a..67fbf22778 100644 > --- a/util/osdep.c > +++ b/util/osdep.c > @@ -33,6 +33,7 @@ > extern int madvise(char *, size_t, int); > #endif > > +#include > #include "qemu-common.h" > #include "qemu/cutils.h" > #include "qemu/sockets.h" > @@ -615,3 +616,23 @@ writev(int fd, const struct iovec *iov, int iov_cnt) > return readv_writev(fd, iov, iov_cnt, true); > } > #endif > + > +struct dirent * > +qemu_dirent_dup(struct dirent *dent) > +{ > + size_t sz = 0; > +#if defined _DIRENT_HAVE_D_RECLEN > + /* Avoid use of strlen() if platform supports d_reclen. */ > + sz = dent->d_reclen; > +#endif > + /* > + * Test sz for zero even if d_reclen is available > + * because some drivers may set d_reclen to zero. > + */ > + if (sz == 0) { > + /* Fallback to the most portable way. */ > + sz = offsetof(struct dirent, d_name) + > + strlen(dent->d_name) + 1; > + } > + return g_memdup(dent, sz); > +}