file: Avoid a read-after-free of fd tables in sysctl handlers
Some loops access the fd table of a different process, and drop the filedesc lock while iterating, so they check the table's refcount. However, we access the table before the first iteration, in order to get the number of table entries, and this access can be a use-after-free. Fix the problem by checking the refcount before we start iterating. Reported by: pho Reviewed by: mjg MFC after: 2 weeks Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D34575
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7846554819
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c702242292
@ -4194,9 +4194,9 @@ sysctl_kern_file(SYSCTL_HANDLER_ARGS)
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if (fdp == NULL)
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continue;
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FILEDESC_SLOCK(fdp);
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if (refcount_load(&fdp->fd_refcnt) == 0)
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goto nextproc;
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FILEDESC_FOREACH_FP(fdp, n, fp) {
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if (refcount_load(&fdp->fd_refcnt) == 0)
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break;
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xf.xf_fd = n;
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xf.xf_file = (uintptr_t)fp;
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xf.xf_data = (uintptr_t)fp->f_data;
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@ -4207,9 +4207,16 @@ sysctl_kern_file(SYSCTL_HANDLER_ARGS)
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xf.xf_offset = foffset_get(fp);
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xf.xf_flag = fp->f_flag;
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error = SYSCTL_OUT(req, &xf, sizeof(xf));
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if (error)
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/*
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* There is no need to re-check the fdtable refcount
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* here since the filedesc lock is not dropped in the
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* loop body.
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*/
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if (error != 0)
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break;
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}
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nextproc:
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FILEDESC_SUNLOCK(fdp);
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fddrop(fdp);
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if (error)
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@ -4469,9 +4476,9 @@ kern_proc_filedesc_out(struct proc *p, struct sbuf *sb, ssize_t maxlen,
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if (pwd != NULL)
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pwd_drop(pwd);
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FILEDESC_SLOCK(fdp);
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if (refcount_load(&fdp->fd_refcnt) == 0)
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goto skip;
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FILEDESC_FOREACH_FP(fdp, i, fp) {
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if (refcount_load(&fdp->fd_refcnt) == 0)
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break;
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#ifdef CAPABILITIES
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rights = *cap_rights(fdp, i);
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#else /* !CAPABILITIES */
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@ -4484,9 +4491,10 @@ kern_proc_filedesc_out(struct proc *p, struct sbuf *sb, ssize_t maxlen,
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* loop continues.
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*/
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error = export_file_to_sb(fp, i, &rights, efbuf);
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if (error != 0)
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if (error != 0 || refcount_load(&fdp->fd_refcnt) == 0)
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break;
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}
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skip:
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FILEDESC_SUNLOCK(fdp);
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fail:
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if (fdp != NULL)
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@ -4633,18 +4641,19 @@ sysctl_kern_proc_ofiledesc(SYSCTL_HANDLER_ARGS)
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if (pwd != NULL)
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pwd_drop(pwd);
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FILEDESC_SLOCK(fdp);
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if (refcount_load(&fdp->fd_refcnt) == 0)
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goto skip;
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FILEDESC_FOREACH_FP(fdp, i, fp) {
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if (refcount_load(&fdp->fd_refcnt) == 0)
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break;
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export_file_to_kinfo(fp, i, NULL, kif, fdp,
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KERN_FILEDESC_PACK_KINFO);
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FILEDESC_SUNLOCK(fdp);
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kinfo_to_okinfo(kif, okif);
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error = SYSCTL_OUT(req, okif, sizeof(*okif));
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FILEDESC_SLOCK(fdp);
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if (error)
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if (error != 0 || refcount_load(&fdp->fd_refcnt) == 0)
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break;
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}
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skip:
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FILEDESC_SUNLOCK(fdp);
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fddrop(fdp);
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pddrop(pdp);
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