git: 4696baaaa95c - stable/12 - UFS2: Fix DoS due to corrupted extattrfile

[Ed Maste]

The branch stable/12 has been updated by emaste:

URL: https://cgit.FreeBSD.org/src/commit/?id=4696baaaa95ce9a75a7b1989474382c85981f805

commit 4696baaaa95ce9a75a7b1989474382c85981f805
Author:     Conrad Meyer <cem at FreeBSD.org>
AuthorDate: 2020-10-30 19:00:42 +0000
Commit:     Ed Maste <emaste at FreeBSD.org>
CommitDate: 2021-01-05 13:56:23 +0000

    UFS2: Fix DoS due to corrupted extattrfile
    
    Prior versions of FreeBSD (11.x) may have produced a corrupt extattr file.
    (Specifically, r312416 accidentally fixed this defect by removing a strcpy.)
    CURRENT FreeBSD supports disk images from those prior versions of FreeBSD.
    Validate the internal structure as soon as we read it in from disk, to
    prevent these extattr files from causing invariants violations and DoS.
    
    Attempting to access the extattr portion of these files results in
    EINTEGRITY.  At this time, the only way to repair files damaged in this way
    is to copy the contents to another file and move it over the original.
    
    PR:             244089
    Reported by:    Andrea Venturoli <ml AT netfence.it>
    Reviewed by:    kib
    Discussed with: mckusick (earlier draft)
    
    (cherry picked from commit e6790841f749b3cc1ac7d338181d9358aae04d0b)
---
 sys/ufs/ffs/ffs_vnops.c | 31 ++++++++++++++++++++-----------
 sys/ufs/ufs/extattr.h   |  2 +-
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/sys/ufs/ffs/ffs_vnops.c b/sys/ufs/ffs/ffs_vnops.c
index d50418fefcad..33f0bb7afedd 100644
--- a/sys/ufs/ffs/ffs_vnops.c
+++ b/sys/ufs/ffs/ffs_vnops.c
@@ -1141,9 +1141,8 @@ ffs_findextattr(u_char *ptr, u_int length, int nspace, const char *name,
 	eap = (struct extattr *)ptr;
 	eaend = (struct extattr *)(ptr + length);
 	for (; eap < eaend; eap = EXTATTR_NEXT(eap)) {
-		/* make sure this entry is complete */
-		if (EXTATTR_NEXT(eap) > eaend)
-			break;
+		KASSERT(EXTATTR_NEXT(eap) <= eaend,
+		    ("extattr next %p beyond %p", EXTATTR_NEXT(eap), eaend));
 		if (eap->ea_namespace != nspace || eap->ea_namelength != nlen
 		    || memcmp(eap->ea_name, name, nlen) != 0)
 			continue;
@@ -1157,8 +1156,9 @@ ffs_findextattr(u_char *ptr, u_int length, int nspace, const char *name,
 }
 
 static int
-ffs_rdextattr(u_char **p, struct vnode *vp, struct thread *td, int extra)
+ffs_rdextattr(u_char **p, struct vnode *vp, struct thread *td)
 {
+	const struct extattr *eap, *eaend, *eapnext;
 	struct inode *ip;
 	struct ufs2_dinode *dp;
 	struct fs *fs;
@@ -1172,10 +1172,10 @@ ffs_rdextattr(u_char **p, struct vnode *vp, struct thread *td, int extra)
 	fs = ITOFS(ip);
 	dp = ip->i_din2;
 	easize = dp->di_extsize;
-	if ((uoff_t)easize + extra > UFS_NXADDR * fs->fs_bsize)
+	if ((uoff_t)easize > UFS_NXADDR * fs->fs_bsize)
 		return (EFBIG);
 
-	eae = malloc(easize + extra, M_TEMP, M_WAITOK);
+	eae = malloc(easize, M_TEMP, M_WAITOK);
 
 	liovec.iov_base = eae;
 	liovec.iov_len = easize;
@@ -1190,7 +1190,17 @@ ffs_rdextattr(u_char **p, struct vnode *vp, struct thread *td, int extra)
 	error = ffs_extread(vp, &luio, IO_EXT | IO_SYNC);
 	if (error) {
 		free(eae, M_TEMP);
-		return(error);
+		return (error);
+	}
+	/* Validate disk xattrfile contents. */
+	for (eap = (void *)eae, eaend = (void *)(eae + easize); eap < eaend;
+	    eap = eapnext) {
+		eapnext = EXTATTR_NEXT(eap);
+		/* Bogusly short entry or bogusly long entry. */
+		if (eap->ea_length < sizeof(*eap) || eapnext > eaend) {
+			free(eae, M_TEMP);
+			return (EINTEGRITY);
+		}
 	}
 	*p = eae;
 	return (0);
@@ -1241,7 +1251,7 @@ ffs_open_ea(struct vnode *vp, struct ucred *cred, struct thread *td)
 		return (0);
 	}
 	dp = ip->i_din2;
-	error = ffs_rdextattr(&ip->i_ea_area, vp, td, 0);
+	error = ffs_rdextattr(&ip->i_ea_area, vp, td);
 	if (error) {
 		ffs_unlock_ea(vp);
 		return (error);
@@ -1549,9 +1559,8 @@ vop_listextattr {
 	eap = (struct extattr *)ip->i_ea_area;
 	eaend = (struct extattr *)(ip->i_ea_area + ip->i_ea_len);
 	for (; error == 0 && eap < eaend; eap = EXTATTR_NEXT(eap)) {
-		/* make sure this entry is complete */
-		if (EXTATTR_NEXT(eap) > eaend)
-			break;
+		KASSERT(EXTATTR_NEXT(eap) <= eaend,
+		    ("extattr next %p beyond %p", EXTATTR_NEXT(eap), eaend));
 		if (eap->ea_namespace != ap->a_attrnamespace)
 			continue;
 
diff --git a/sys/ufs/ufs/extattr.h b/sys/ufs/ufs/extattr.h
index 68b6a424e563..20d3401e68bf 100644
--- a/sys/ufs/ufs/extattr.h
+++ b/sys/ufs/ufs/extattr.h
@@ -95,7 +95,7 @@ struct extattr {
  *	content referenced by eap.
  */
 #define	EXTATTR_NEXT(eap) \
-	((struct extattr *)(((u_char *)(eap)) + (eap)->ea_length))
+	((struct extattr *)(__DECONST(char *, (eap)) + (eap)->ea_length))
 #define	EXTATTR_CONTENT(eap) \
 	(void *)(((u_char *)(eap)) + EXTATTR_BASE_LENGTH(eap))
 #define	EXTATTR_CONTENT_SIZE(eap) \