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[83.50.83.154]) by smtp.gmail.com with ESMTPSA id g22sm6148779pfc.177.2022.02.05.03.58.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 05 Feb 2022 03:58:27 -0800 (PST) Message-ID: <83e8e341-4226-9ee6-018b-8bdb03e8ffef@amsat.org> Date: Sat, 5 Feb 2022 12:58:23 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.5.1 Subject: Re: [PATCH v3] 9pfs: Fix segfault in do_readdir_many caused by struct dirent overread Content-Language: en-US To: Christian Schoenebeck , qemu-devel@nongnu.org Cc: Vitaly Chikunov , Greg Kurz , qemu-stable@nongnu.org, ldv@altlinux.org References: <20220204050609.15510-1-vt@altlinux.org> <2519450.KGbbELgHQX@silver> In-Reply-To: <2519450.KGbbELgHQX@silver> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Host-Lookup-Failed: Reverse DNS lookup failed for 2607:f8b0:4864:20::433 (failed) Received-SPF: pass client-ip=2607:f8b0:4864:20::433; envelope-from=philippe.mathieu.daude@gmail.com; helo=mail-pf1-x433.google.com X-Spam_score_int: -6 X-Spam_score: -0.7 X-Spam_bar: / X-Spam_report: (-0.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FORGED_FROMDOMAIN=0.249, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.249, NICE_REPLY_A=-0.001, PDS_HP_HELO_NORDNS=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RDNS_NONE=0.793, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no 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" Reply-to: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= via On 5/2/22 12:36, Christian Schoenebeck wrote: > On Freitag, 4. Februar 2022 06:06:09 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, 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 >> Signed-off-by: Vitaly Chikunov >> --- >> Tested on x86-64 Linux again. >> >> Changes from v2: >> - Make it work with a simulated dirent where d_reclen is 0, which was >> caused abort in readdir qos-test, by using fallback at runtime. >> >> hw/9pfs/codir.c | 3 +-- >> include/qemu/osdep.h | 13 +++++++++++++ >> util/osdep.c | 18 ++++++++++++++++++ >> 3 files changed, 32 insertions(+), 2 deletions(-) >> >> 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..2c80528a61 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 +616,20 @@ 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 there's d_reclen. */ >> + sz = dent->d_reclen; >> +#endif >> + if (sz == 0) { > > Philippe, Greg, apart from the additional comment, do you want to see this > check to be changed in v4 to this? > > if (unlikely(sz == 0)) { This is not an hot path so probably not very useful. > > Best regards, > Christian Schoenebeck > >> + /* Fallback to the most portable way. */ >> + sz = offsetof(struct dirent, d_name) + >> + strlen(dent->d_name) + 1; >> + } >> + struct dirent *dst = g_malloc(sz); >> + return memcpy(dst, dent, sz); However 'return g_memdup(dent, sz)' is simpler to review. >> +} > > >