The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=d91c459a93e5f70c1d3ad3d504bcf64babed8600
commit d91c459a93e5f70c1d3ad3d504bcf64babed8600 Author: Alan Somers <[email protected]> AuthorDate: 2026-05-04 19:35:11 +0000 Commit: Mark Johnston <[email protected]> CommitDate: 2026-05-20 19:34:50 +0000 fusefs: Handle buggy servers' LISTXATTR response The fuse protocol requires server to respond to LISTXATTR with a NUL-terminated string. If they don't, report an error rather than attempt to scan through uninitialized memory for a NUL. Approved by: so Security: FreeBSD-SA-26:20.fusefs Security: CVE-2026-45252 admbugs: 1039 Reported by: Joshua Rogers Sponsored by: ConnectWise --- sys/fs/fuse/fuse_ipc.h | 1 + sys/fs/fuse/fuse_vnops.c | 18 +++++++---- tests/sys/fs/fusefs/xattr.cc | 73 ++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 86 insertions(+), 6 deletions(-) diff --git a/sys/fs/fuse/fuse_ipc.h b/sys/fs/fuse/fuse_ipc.h index 8ceb6bb1fb1a..7091296bb453 100644 --- a/sys/fs/fuse/fuse_ipc.h +++ b/sys/fs/fuse/fuse_ipc.h @@ -240,6 +240,7 @@ struct fuse_data { #define FSESS_WARN_INODE_MISMATCH 0x4000000 /* ino != nodeid */ #define FSESS_SETXATTR_EXT 0x8000000 /* extended fuse_setxattr_in */ #define FSESS_AUTO_UNMOUNT 0x10000000 /* perform unmount when server dies */ +#define FSESS_WARN_LSEXTATTR_NUL 0x20000000 /* Non nul-terminated xattr list */ #define FSESS_MNTOPTS_MASK ( \ FSESS_DAEMON_CAN_SPY | FSESS_PUSH_SYMLINKS_IN | \ FSESS_DEFAULT_PERMISSIONS | FSESS_INTR | FSESS_AUTO_UNMOUNT) diff --git a/sys/fs/fuse/fuse_vnops.c b/sys/fs/fuse/fuse_vnops.c index dd3cc5f16092..d1badd0700f8 100644 --- a/sys/fs/fuse/fuse_vnops.c +++ b/sys/fs/fuse/fuse_vnops.c @@ -2978,8 +2978,8 @@ out: * bsd_list, bsd_list_len - output list compatible with bsd vfs */ static int -fuse_xattrlist_convert(char *prefix, const char *list, int list_len, - char *bsd_list, int *bsd_list_len) +fuse_xattrlist_convert(struct fuse_data *data, char *prefix, const char *list, + int list_len, char *bsd_list, int *bsd_list_len) { int len, pos, dist_to_next, prefix_len; @@ -2988,7 +2988,14 @@ fuse_xattrlist_convert(char *prefix, const char *list, int list_len, prefix_len = strlen(prefix); while (pos < list_len && list[pos] != '\0') { - dist_to_next = strlen(&list[pos]) + 1; + dist_to_next = strnlen(&list[pos], list_len - pos - 1) + 1; + if (list[pos + dist_to_next - 1] != '\0') { + fuse_warn(data, FSESS_WARN_LSEXTATTR_NUL, + "The FUSE server returned a non nul-terminated " + "LISTXATTR response."); + return (EXTERROR(EIO, + "The FUSE server returned a malformed list")); + } if (bcmp(&list[pos], prefix, prefix_len) == 0 && list[pos + prefix_len] == extattr_namespace_separator) { len = dist_to_next - @@ -3044,6 +3051,7 @@ fuse_vnop_listextattr(struct vop_listextattr_args *ap) struct fuse_listxattr_in *list_xattr_in; struct fuse_listxattr_out *list_xattr_out; struct mount *mp = vnode_mount(vp); + struct fuse_data *data = fuse_get_mpdata(mp); struct thread *td = ap->a_td; struct ucred *cred = ap->a_cred; char *prefix; @@ -3124,8 +3132,6 @@ fuse_vnop_listextattr(struct vop_listextattr_args *ap) linux_list = fdi.answ; /* FUSE doesn't allow the server to return more data than requested */ if (fdi.iosize > linux_list_len) { - struct fuse_data *data = fuse_get_mpdata(mp); - fuse_warn(data, FSESS_WARN_LSEXTATTR_LONG, "server returned " "more extended attribute data than requested; " @@ -3142,7 +3148,7 @@ fuse_vnop_listextattr(struct vop_listextattr_args *ap) * FreeBSD's format before giving it to the user. */ bsd_list = malloc(linux_list_len, M_TEMP, M_WAITOK); - err = fuse_xattrlist_convert(prefix, linux_list, linux_list_len, + err = fuse_xattrlist_convert(data, prefix, linux_list, linux_list_len, bsd_list, &bsd_list_len); if (err != 0) goto out; diff --git a/tests/sys/fs/fusefs/xattr.cc b/tests/sys/fs/fusefs/xattr.cc index afeacd4a249e..6dfda55079eb 100644 --- a/tests/sys/fs/fusefs/xattr.cc +++ b/tests/sys/fs/fusefs/xattr.cc @@ -492,6 +492,79 @@ TEST_F(ListxattrSig, erange_forever) ASSERT_TRUE(WIFSIGNALED(status)); } +/* + * A buggy or malicious server returns a list that isn't nul-terminated. The + * kernel should handle it gracefully. + */ +TEST_F(Listxattr, not_nul_terminated) +{ + uint64_t ino = 42; + int ns = EXTATTR_NAMESPACE_USER; + char *data; + const char expected[4] = {3, 'f', 'o', 'o'}; + const char first[255] = "user.foo\0system.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"; + const uint8_t badlist[9] = {'u', 's', 'e', 'r', '.', 'f', 'o', 'o', 'd'}; + Sequence seq; + + EXPECT_LOOKUP(FUSE_ROOT_ID, RELPATH) + .WillRepeatedly(Invoke( + ReturnImmediate([=](auto in __unused, auto& out) { + SET_OUT_HEADER_LEN(out, entry); + out.body.entry.attr.mode = S_IFREG | 0644; + out.body.entry.nodeid = ino; + out.body.entry.attr.nlink = 1; + out.body.entry.attr_valid = UINT64_MAX; + out.body.entry.entry_valid = UINT64_MAX; + }))); + + /* + * On the first LISTXATTRS call, return a big attribute just to fill + * the heap with non-NUL data. + */ + expect_listxattr(ino, 0, + ReturnImmediate([&](auto in __unused, auto& out) { + out.body.listxattr.size = sizeof(first); + SET_OUT_HEADER_LEN(out, listxattr); + }), &seq + ); + expect_listxattr(ino, sizeof(first), + ReturnImmediate([&](auto in __unused, auto& out) { + memcpy((void*)out.body.bytes, first, sizeof(first)); + out.header.len = sizeof(fuse_out_header) + sizeof(first); + }), &seq + ); + /* + * On the second LISTXATTRS call, return a malformed list with no NUL + * termination. The heap might still be full of the data from the + * first call. + */ + expect_listxattr(ino, 0, + ReturnImmediate([&](auto in __unused, auto& out) { + out.body.listxattr.size = sizeof(badlist); + SET_OUT_HEADER_LEN(out, listxattr); + }), &seq + ); + expect_listxattr(ino, sizeof(badlist), + ReturnImmediate([&](auto in __unused, auto& out) { + memset((void*)out.body.bytes, 'x', sizeof(first)); + memcpy((void*)out.body.bytes, badlist, sizeof(badlist)); + out.header.len = sizeof(fuse_out_header) + sizeof(badlist); + }), &seq + ); + + data = new char[1024]; + + ASSERT_EQ(static_cast<ssize_t>(sizeof(expected)), + extattr_list_file(FULLPATH, ns, data, sizeof(data))) + << strerror(errno); + /* + * Receiving this malformed list, the kernel should log it to dmesg and + * report an IO error to the caller. + */ + ASSERT_EQ(-1, extattr_list_file(FULLPATH, ns, data, sizeof(data))); + EXPECT_EQ(EIO, errno); +} + /* * Get the size of the list that it would take to list no extended attributes */
