9pfs: Fix segfault in do_readdir_many caused by struct dirent overread
`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 <qemu_oss@crudebyte.com> Reviewed-by: Dmitry V. Levin <ldv@altlinux.org> Signed-off-by: Vitaly Chikunov <vt@altlinux.org> Tested-by: Christian Schoenebeck <qemu_oss@crudebyte.com> Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com> Acked-by: Greg Kurz <groug@kaod.org> Tested-by: Vitaly Chikunov <vt@altlinux.org> Message-Id: <20220216181821.3481527-1-vt@altlinux.org> [C.S. - Fix typo in source comment. ] Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
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@ -182,7 +182,12 @@ static int synth_opendir(FsContext *ctx,
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V9fsSynthOpenState *synth_open;
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V9fsSynthOpenState *synth_open;
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V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data;
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V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data;
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synth_open = g_malloc(sizeof(*synth_open));
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/*
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* V9fsSynthOpenState contains 'struct dirent' which have OS-specific
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* properties, thus it's zero cleared on allocation here and below
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* in synth_open.
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*/
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synth_open = g_new0(V9fsSynthOpenState, 1);
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synth_open->node = node;
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synth_open->node = node;
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node->open_count++;
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node->open_count++;
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fs->private = synth_open;
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fs->private = synth_open;
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@ -220,7 +225,14 @@ static void synth_rewinddir(FsContext *ctx, V9fsFidOpenState *fs)
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static void synth_direntry(V9fsSynthNode *node,
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static void synth_direntry(V9fsSynthNode *node,
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struct dirent *entry, off_t off)
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struct dirent *entry, off_t off)
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{
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{
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strcpy(entry->d_name, node->name);
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size_t sz = strlen(node->name) + 1;
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/*
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* 'entry' is always inside of V9fsSynthOpenState which have NAME_MAX
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* back padding. Ensure we do not overflow it.
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*/
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g_assert(sizeof(struct dirent) + NAME_MAX >=
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offsetof(struct dirent, d_name) + sz);
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memcpy(entry->d_name, node->name, sz);
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entry->d_ino = node->attr->inode;
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entry->d_ino = node->attr->inode;
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entry->d_off = off + 1;
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entry->d_off = off + 1;
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}
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}
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@ -266,7 +278,7 @@ static int synth_open(FsContext *ctx, V9fsPath *fs_path,
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V9fsSynthOpenState *synth_open;
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V9fsSynthOpenState *synth_open;
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V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data;
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V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data;
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synth_open = g_malloc(sizeof(*synth_open));
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synth_open = g_new0(V9fsSynthOpenState, 1);
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synth_open->node = node;
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synth_open->node = node;
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node->open_count++;
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node->open_count++;
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fs->private = synth_open;
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fs->private = synth_open;
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@ -41,6 +41,11 @@ typedef struct V9fsSynthOpenState {
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off_t offset;
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off_t offset;
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V9fsSynthNode *node;
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V9fsSynthNode *node;
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struct dirent dent;
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struct dirent dent;
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/*
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* Ensure there is enough space for 'dent' above, some systems have a
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* d_name size of just 1, which would cause a buffer overrun.
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*/
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char dent_trailing_space[NAME_MAX];
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} V9fsSynthOpenState;
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} V9fsSynthOpenState;
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int qemu_v9fs_synth_mkdir(V9fsSynthNode *parent, int mode,
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int qemu_v9fs_synth_mkdir(V9fsSynthNode *parent, int mode,
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@ -143,8 +143,7 @@ static int do_readdir_many(V9fsPDU *pdu, V9fsFidState *fidp,
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} else {
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} else {
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e = e->next = g_malloc0(sizeof(V9fsDirEnt));
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e = e->next = g_malloc0(sizeof(V9fsDirEnt));
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}
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}
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e->dent = g_malloc0(sizeof(struct dirent));
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e->dent = qemu_dirent_dup(dent);
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memcpy(e->dent, dent, sizeof(struct dirent));
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/* perform a full stat() for directory entry if requested by caller */
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/* perform a full stat() for directory entry if requested by caller */
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if (dostat) {
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if (dostat) {
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@ -805,6 +805,19 @@ static inline int platform_does_not_support_system(const char *command)
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}
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}
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#endif /* !HAVE_SYSTEM_FUNCTION */
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#endif /* !HAVE_SYSTEM_FUNCTION */
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/**
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* Duplicate directory entry @dent.
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*
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* It is highly recommended to use this function instead of open coding
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* duplication of @c dirent objects, because the actual @c struct @c dirent
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* size may be bigger or shorter than @c sizeof(struct dirent) and correct
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* handling is platform specific (see gitlab issue #841).
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*
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* @dent - original directory entry to be duplicated
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* @returns duplicated directory entry which should be freed with g_free()
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*/
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struct dirent *qemu_dirent_dup(struct dirent *dent);
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#ifdef __cplusplus
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#ifdef __cplusplus
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}
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}
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#endif
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#endif
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21
util/osdep.c
21
util/osdep.c
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@ -33,6 +33,7 @@
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extern int madvise(char *, size_t, int);
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extern int madvise(char *, size_t, int);
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#endif
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#endif
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#include <dirent.h>
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#include "qemu-common.h"
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#include "qemu-common.h"
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#include "qemu/cutils.h"
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#include "qemu/cutils.h"
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#include "qemu/sockets.h"
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#include "qemu/sockets.h"
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@ -615,3 +616,23 @@ writev(int fd, const struct iovec *iov, int iov_cnt)
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return readv_writev(fd, iov, iov_cnt, true);
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return readv_writev(fd, iov, iov_cnt, true);
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}
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}
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#endif
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#endif
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struct dirent *
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qemu_dirent_dup(struct dirent *dent)
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{
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size_t sz = 0;
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#if defined _DIRENT_HAVE_D_RECLEN
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/* Avoid use of strlen() if platform supports d_reclen. */
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sz = dent->d_reclen;
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#endif
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/*
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* Test sz for zero even if d_reclen is available
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* because some drivers may set d_reclen to zero.
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*/
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if (sz == 0) {
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/* Fallback to the most portable way. */
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sz = offsetof(struct dirent, d_name) +
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strlen(dent->d_name) + 1;
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}
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return g_memdup(dent, sz);
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}
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